"The Other Bennet Sister" is Closer to Jane Eyre than Jane Austen:

Once upon a time there was a girl born without the gift of beauty, grace, the pleasing manners of extroverts, or the prospect of a fortune. Always criticized and compared unfavorably to her counterparts -- when she got any notice at all -- she grew up lonely with little hope for finding happiness. Once she was grown up, she determined to leave what she had known and comes to find a true home, self-acceptance, and the love she deserved,  despite never blossoming into a beauty. After turning down a proposal from a handsome suitor, she finally got to marry the man she had been in love with who was unattainable for a time.

 Coaster in" The Other Bennet Sister" collection 

That's a summary of Janice Hadlow's 2020 novel, The Other Bennet Sister. Add in a bit about taking on the role of governess, and you have the 2026 adaption's version of the story. Of course, it's also the summary of Jane Eyre's story. Without the inspiration and model set by Charlotte Brontë to apply Romanticism to the novel form and give voice to the type of women never before cast as heroines, this kind of coming-of-age story would not have been possible.  

Romantic aspirations meet everyday reality

While Jane Austen lived during the Romantic movement, she is not generally counted among the Romantics. She may have heard of Blake, Wordsworth, Coleridge, Keats, Byron, and Shelley, but she definitely does not quote them. Her references to the picturesque or sensibility should not be mistaken for Romanticism, as she draws on artistic movement from the 18th century.  

In The Other Bennet Sister, Wordsworth's poetry is central to Tom Hayward's character. He shares it with Mary who comes to appreciate experiencing landscapes as a poet does, not just reciting lines, but feeling them. Like him, she internalizes that Romantic quality, and it becomes part of her self-discovery that make it possible for her to feel the happiness she has not experienced when she turned to books for direction and identity at Longbourn.  

It is a very compelling story that resonates well with readers and audiences in the 2020s.  But it deviates from Jane Austen's heroines' stories in a number of ways.

1.All of  Austen's heroines are -- if not beautiful -- handsome enough to be tempting. That holds true even of Anne Elliot who had felt herself aged and faded at 27 but blooms back into good looks, as well as of Fanny Price who becomes decidedly attractive when she grows up. 

2.  Austen's heroines do tend to take some kind of journey and sometimes enjoy being outside to admire the view or for a picnic, but their form of nature is typically very much contained.

3. Austen maintains that men always make the first move as far as declarations of feeling.

4. None of Austen's heroines ever have to earn a living. 

A different take on what's interesting

“[Charlotte Brontë] once told her sisters that they were wrong - even morally wrong - in making their heroines beautiful as a matter of course. They replied that it was impossible to make a heroine interesting on any other terms. Her answer was, 'I will prove to you that you are wrong; I will show you a heroine as plain and as small as myself, who shall be as interesting as any of yours.”

― Elizabeth Gaskell, The Life of Charlotte Brontë

It wasn't just Charlotte's sister, Emily and Anne, who believed in the general rule of beautiful heroines. It had been a tradition reinforced by the author that George Lewes (the man that George Eliot lived with because he already had a wife)  told  Charlotte to take as her model, Jane Austen. Brontë began here response with an indication she would try to take his advice to heart and be "more subdued," but she quickly proves she has no intention of doing so as preserved Gaskell's biography:

"Why do you like Miss Austen so very much? I am puzzled on that point. What induced you to say that you would have rather written Pride and Prejudice, or Tom Jones, than any of the Waverley Novels?

"I had not seen Pride and Prejudice till I read that sentence of yours, and then I got the book. And what did I find ? An accurate, daguerreotyped portrait of a commonplace face a carefully-fenced, highly-cultivated garden, with neat borders and delicate flowers; but no glance of a bright, vivid physiognomy, no open country, no fresh air, no blue hill, no bonny beck. I should hardly like to live with her ladies and gentlemen, in their elegant but confined houses.

If you think about it, you realize that Austen's landscapes are very much as Brontë  describes them. They are tamed and circumscribed and utterly devoid of the sublime quality that the Romantics attempted to capture through their art. But that's not the case in The Other Bennet Sister in which Mary Bennet travels to the Lake District and ventures on a climb to experience the sublime for herself. She even refuses to listen to reason when the guide warns of a storm brewing, going along with Ryder's suggestion that they experience it instead of escape it. (In the book the consequences are just a miserably wet descent, though the adaption has Mary fall deathly ill as a result to allow for some elements from  Sense and Sensibility.)  

Can a heroine speak freely? 

In Austen's universe, the answer is no. The heroines have to hold back to maintain decorum and their dignity. That is central to the story of Elinor Dashwood, Fanny Price, and Anne Elliot. But what of Mary Bennet? In the novel devoted to her, this is the crux of the matter. Her path was already paved by Jane Austen who expresses herself passionately and freely to Rochester:

"Do you think I can stay to become nothing to you? Do you think I am an automaton?--a machine without feelings? and can bear to have my morsel of bread snatched from my lips, and my drop of living water dashed from my cup? Do you think, because I am poor, obscure, plain, and little, I am soulless and heartless? You think wrong!--I have as much soul as you,--and full as much heart! And if God had gifted me with some beauty and much wealth, I should have made it as hard for you to leave me, as it is now for me to leave you. I am not talking to you now through the medium of custom, conventionalities, nor even of mortal flesh;--it is my spirit that addresses your spirit; just as if both had passed through the grave, and we stood at God's feet, equal,--as we are!"
-Charlotte Brontë, Jane Eyre (chapter 23)

Jane knows she doesn't look like a heroine, being "poor, obscure, plain, and little," though that doesn't mean she doesn't have the soul and heart of one.  Romantic that she is, she insist on not confining herself to "the medium of custom, conventionalities" that are the very fabric of the Austenian universe to be able to address Rochester (who was her employer and social superior) as her equal.

from "The Other Bennet Sister" collection 

All or bust

As all readers of Pride and Prejudice know, Charlotte Lucas  she determines to win the attention of Mr. Collins and marry him to assure herself of a secure future -- if not a very happy one.. She appears to be an older version of Mary -- plain and penniless --just without spectacles. At 27, she realizes she may never get another opportunity for matrimony. Someone like her would never attract someone like Mr. Darcy and so she takes what she can get. 

Mary Bennet finds herself with the unexpected opportunity to make a far more brilliant match than Charlotte does  when the handsome, charming, and rich Mr. Ryder  proposes to her. Of course, he doesn't propose at first. He just suggests she accompany him to Italy. Before it has quite dawned on her what that would mean without marriage, Mary already tells him she cannot accept because she doesn't love him.   

In the very next chapter he does propose.  and then even offers to tell Mary what his motivation is on p. 425: 

"There are all the usual reasons of course. I enjoy your company. I find you kind, unaffected, modest, and charming... But I must tell you, there is a more selfish dimension to my preference. I think you would improve me. You are serious where I am flighty. You work hard where I am lazy. You think deeply where I am shallow. Thing what a good deed you would do in marrying me. Imagine how your influence would change me for the betters. Perhaps, for those reasons, if for no other, you are obliged to accept me?"

Though he is not as insistent as St. John Reed is in pressing Jane Eyre to marry him because it is her duty to support him in his mission to India, he still is making the argument that a woman is obligated to marry a man she does not love out of duty.

Thinking about why she had no choice other than to reject Ryder's proposal in chapter 91 on p. 434, Mary muses: "If she had known nothing else -- if she had never had a hint of what real love looked like, she might have been content with the pale facsimile of happiness a pragmatic marriage offered. but now that she had known Mr. Hayward, it would not do. Now that she had met a man she truly loved, she could not marry another." 

That is very similar to what Jane put in more defiant terms in resisting St. John. In chapter 34, when she tells him: "I scorn your idea of love," and continues, "I scorn the counterfeit sentiment you offer."  

Even as her own will starts to weaken, she knows this is not the love she has experienced, as she says in chapter 35: "He pressed his hand firmer on my head, as if he claimed me: he surrounded me with his arm, almost as if he loved me (I say almost — I knew the difference — for I had felt what it was to be loved; but, like him, I had now put love out of the question, and thought only of duty)." Jane nearly succumbs to St. John and only gains the strength to break away when she hears a voice call her name.

Mary doesn't have any such supernatural inspiration but her own resolve to continue to wait for Tom Hayward rather than settle for anything else because, as she tells him when he finally does return in chapter 92 p. 452: "I have loved you for a very long time and know I will never love anyone as much as I love you. You are the only man who could ever make me happy, and I have missed you -- oh, I have missed you so very, very much." 

Even before this confession, Mary repeatedly thinks about her happiness depending completely on a future with Tom Hayward and chafes at being banned from seeking him out to tell him so by the conventionalities of society. There is a lot of pent-up frustration behind this moment in which she rebels against  social norms that in confessing her love to him before he makes his own declaration. Austen would not endorse that, but Brontë.

A nod to Villette

The adaption takes on a somewhat different direction about how Mary defines her life direction that I'm not even certain audiences who get carried away by seeing their "ships" come together would notice. While Tom was absent, she pursued her plan to be what she calls a governess but is really a tutor, something she intends to continue after her marriage. 

This runs completely counter to the book in which Lady Catherine's suggestion that Mary become a governess fills her with horror and prompts her to escape that fate by staying with the Gardiners indefinitely.  The way Mary regards the prospect of being a governess in the book is much more consistent with Austen's view, which she gives voice to in Emma the character of Jane Fairfax. 

But to a modern audience, it makes sense that a woman who has devoted much of her love to acquiring learning may wish to share that with other in order to feel fulfilled. The Sanditon adaption also showed its heroine working as a governess and even continuing to teach after marriage when she didn't need to make a living. In reality, that would not have been socially accepted. Only spinsters could have continued working.

The adaption is really upholding 21st century views that women are entitled to a career that makes them feel fulfilled. But there was some precedent to this in another Brontë heroine: Lucy Snowe. Like Jane Eyre, Lucy has no fortune or looks to recommend her and must make her own way in the world. She does this by teaching and even works her way up to establishing her own school. The narrator suggests that the school was not going to be abandoned upon marriage, which was a pretty bold take for that time. 

"I write..." mousepad

To read more about the Romantic movement's deep influence on  Brontë's writing, read my dissertation: "Engendering Romanticism: A Study of Charlotte Brontë's Novels"

Related:
Mary and Marylin: the Girl in the Glasses Finds Love

Jane Austen at 250

Jane Austen: Love and Money
Jane Austen at the Morgan
Love and Limerence in Jane Austen
Observations on Jane Austen's Emma
Pride, Prejudice and Persuasion: Obstacles to Happiness in Jane Austen's Novels
Three Janes, Two Governesses, and the Abolitionist Movement
The Big Bow-wow & Bit of Ivory
Jane Austen's Heroines
Jane Austen and Capability Brown
Pride and Prejudice in Job Applications