Mansfield Park: how is Mary Crawford different from Jane Austen’s heroines?

If anyone asks me to compare between Jane Austen and George Eliot, I would say, Middlemarch is a novel of great scope and depth, a good contender for the title of greatest English novel, but Mansfield Park is the reason I place Jane Austen above George Eliot as an artist. She allows 2 characters of whom she disapproves to be immensely attractive and charming, and lays a trap for unsuspecting readers, whereas George Eliot would have made sure, through the moralising narrator, that readers would never side with Henry and Mary Crawford.  
So far I’ve written enough about Henry Crawford. Let’s talk about Mary. 
It’s easy to see why many people like Mary Crawford. She is cheerful, lively, animated, playful, outspoken, and extremely charismatic. Some readers might also see themselves in her because she likes variety and excitement, or when she’s careless and does something deemed inappropriate by the “priggish” Edmund and Fanny. 
Mary Crawford and Fanny Price have 2 things in common. 1, both love Edmund, and are loved by Edmund. 2, both are highly perceptive, and good judges of character. 
Mary notices everything. She sees her uncle, the Admiral, as a man of vices, and knows that her aunt is ill-used. She sees through Dr Grant: 

““…And though Dr. Grant is most kind and obliging to me, and though he is really a gentleman, and, I dare say, a good scholar and clever, and often preaches good sermons, and is very respectable, I see him to be an indolent, selfish bon vivant, who must have his palate consulted in everything; who will not stir a finger for the convenience of any one; and who, moreover, if the cook makes a blunder, is out of humour with his excellent wife. To own the truth, Henry and I were partly driven out this very evening by a disappointment about a green goose, which he could not get the better of. My poor sister was forced to stay and bear it.”” (Ch.11)  

She knows that both Maria and Julia are in love with Henry, which escapes almost everyone else apart from him and Fanny. She understands Henry better than he does himself—knowing his love for Fanny wouldn’t last.  
She personally knows many bad marriages and sees through them all, such as the Frasers and the Stornaways. She clearly understands why Maria marries Mr Rushworth. In her turn, Mary falls in love with a kind, good man—Edmund Bertram. And she recognises Fanny’s qualities. 
(Imagine Mary Crawford and Emma Woodhouse in the same book). 
In short, like Fanny, Mary is a good judge of character, and notices many things that escape everyone else at Mansfield Park (and Sotherton). The difference between the 2 characters is that Fanny feels for others, whereas Mary doesn’t care. 
Mary’s main faults are her selfishness, insincerity, and lack of regard for others.  
Early on, there’s a scene where Mary complains about the inconvenience of not having anything to transport her harp: 

““I am to have it to-morrow; but how do you think it is to be conveyed? Not by a wagon or cart: oh no! nothing of that kind could be hired in the village. I might as well have asked for porters and a handbarrow.”
“You would find it difficult, I dare say, just now, in the middle of a very late hay harvest, to hire a horse and cart?”
“I was astonished to find what a piece of work was made of it! To want a horse and cart in the country seemed impossible, so I told my maid to speak for one directly; and as I cannot look out of my dressing-closet without seeing one farmyard, nor walk in the shrubbery without passing another, I thought it would be only ask and have, and was rather grieved that I could not give the advantage to all. Guess my surprise, when I found that I had been asking the most unreasonable, most impossible thing in the world; had offended all the farmers, all the labourers, all the hay in the parish! As for Dr. Grant's bailiff, I believe I had better keep out of his way; and my brother-in-law himself, who is all kindness in general, looked rather black upon me when he found what I had been at.”” (Ch.6) 

She doesn’t stop there: 

““I shall understand all your ways in time; but, coming down with the true London maxim, that everything is to be got with money, I was a little embarrassed at first by the sturdy independence of your country customs…””(ibid.)   

This says a lot about her. To Mary, her own convenience is more important than the farmers’ need for carts during harvest. 
Other little details reveal Mary’s character. She speaks badly of her uncle in front of strangers, and make sweeping generalisations about the Navy and the clergy. She knows the impropriety of private theatricals, and knows Sir Thomas would disapprove, but doesn’t feel bothered. Later, she speaks disrespectfully of Sir Thomas in front of Fanny. 
She doesn’t care when Henry toys with the feelings of Maria and Julia and succeeds at making them both fall in love with him. She doesn’t stop him from trying to “make a small hole in Fanny’s heart”, and even assists him in lying to her about the necklace. Later on, she encourages Fanny to accept Henry, and alludes to the promotion to put pressure on her, despite knowing her own brother’s character and doubting his constancy.
There are 2 moments that are particularly telling. The 1st time is when Mary acknowledges Henry’s flirtatiousness, but defends him anyway: 

““Ah! I cannot deny it. He has now and then been a sad flirt, and cared very little for the havoc he might be making in young ladies' affections. I have often scolded him for it, but it is his only fault; and there is this to be said, that very few young ladies have any affections worth caring for. And then, Fanny, the glory of fixing one who has been shot at by so many; of having it in one's power to pay off the debts of one's sex! Oh! I am sure it is not in woman's nature to refuse such a triumph.”
Fanny shook her head. “I cannot think well of a man who sports with any woman's feelings; and there may often be a great deal more suffered than a stander-by can judge of.”
“I do not defend him. I leave him entirely to your mercy, and when he has got you at Everingham, I do not care how much you lecture him. But this I will say, that his fault, the liking to make girls a little in love with him, is not half so dangerous to a wife's happiness as a tendency to fall in love himself, which he has never been addicted to. And I do seriously and truly believe that he is attached to you in a way that he never was to any woman before…””(Ch.36)  

Note that Mary thinks Fanny is distrustful of his loyalty, and thinks that as long as Henry doesn’t fall in love himself, that’s enough to assure her, whilst Fanny is saying “there may often be a great deal more suffered than a stander-by can judge of”, which is about other women’s feelings. Mary can’t think in such terms because she only cares about herself (and her brother).  
When the Henry-Maria affair is exposed: 

““Their substance was great anger at the folly of each. She reprobated her brother's folly in being drawn on by a woman whom he had never cared for, to do what must lose him the woman he adored; but still more the folly of poor Maria, in sacrificing such a situation, plunging into such difficulties, under the idea of being really loved by a man who had long ago made his indifference clear.”” (Ch.44) 

(This is Edmund telling Fanny about his talk with Mary). 
Again, Mary tries to downplay the seriousness of the betrayal by saying that Henry doesn’t care for Maria, not realising that that is much worse. 
To Edmund, she even blames Fanny:  

““Why would not she have him? It is all her fault. Simple girl! I shall never forgive her. Had she accepted him as she ought, they might now have been on the point of marriage, and Henry would have been too happy and too busy to want any other object. He would have taken no pains to be on terms with Mrs. Rushworth again. It would have all ended in a regular standing flirtation, in yearly meetings at Sotherton and Everingham.”” (ibid.) 

(my emphasis) 
Look at that. These 2 moments say everything you need to know about Mary Crawford, I don’t even need to mention the fact that she wishes Tom Bertram to die so Edmund can be the new heir. 
I’m puzzled that there are people who call themselves Janeites and prefer Mary to Fanny. Tony Tanner writes in his introduction “More than one critic has suggested that Mary Crawford, with her quick wit, her vitality and resilience, is much more like Jane Austen herself than is the shrinking Fanny” (he doesn’t agree, by the way). What a joke. 
Jane Austen’s trap in Mansfield Park is creating Mary Crawford as superficially very similar to the witty, vivacious Elizabeth Bennet, but the similarity is only on the surface. Many readers don’t seem to realise that Elizabeth Bennet and Emma Woodhouse and all of Jane Austen heroines, different as they are, all share a capacity for self-reflection, delicacy, and regard for others. 
Elizabeth Bennet may be proud and make hasty judgment, but she has self-reflection and realises her mistakes. Emma Woodhouse may misread everything, commit errors, and hurt people, but she means well and her mistakes are results of misguided helpfulness rather than malice; she has a bad conscience when realising she has harmed Harriet, hurt Miss Bates, and upset Jane Fairfax, and she changes. The ability to reflect on one’s actions and acknowledge one’s mistakes is highly valued in Jane Austen—understanding, self-awareness, and regard for others are a constant subject in the 6 novels. 
(The word “aware” appears 14 times in Pride and Prejudice, 26 times in Emma, and 40 times in Mansfield Park. Also in Mansfield Park, the word “delicacy” appears 26 times). 
Mary Crawford doesn’t have these qualities. She is self-centred, mercenary, insincere, and manipulative. She doesn’t care about anyone but herself, and has no self-reflection. 
To the readers who love Mary for her wit, Jane Austen has this to say: 

“Wisdom is better than Wit, & in the long run will certainly have the laugh on her side.” (letter to her niece Fanny Knight)