On Amy Dorrit, or how Dickens improves himself

Amy Dorrit can be infuriating. She allows other family members to make unfair accusations about her, almost without protesting. She doesn’t argue, doesn’t explain herself, and doesn’t voice her thoughts. 
For the 1st half of the book, there is barely an outburst from Amy, or expression of annoyance. 
But as I read on, Amy becomes better, and more real. 
This is the 1st moment: 

“Little Dorrit had been thinking too. After softly putting his grey hair aside, and touching his forehead with her lips, she looked towards Arthur, who came nearer to her, and pursued in a low whisper the subject of her thoughts.
‘Mr Clennam, will he pay all his debts before he leaves here?’
‘No doubt. All.’
‘All the debts for which he had been imprisoned here, all my life and longer?’
‘No doubt.’
There was something of uncertainty and remonstrance in her look; something that was not all satisfaction. He wondered to detect it, and said:
‘You are glad that he should do so?’
‘Are you?’ asked Little Dorrit, wistfully.
‘Am I? Most heartily glad!’
‘Then I know I ought to be.’
‘And are you not?’
‘It seems to me hard,’ said Little Dorrit, ‘that he should have lost so many years and suffered so much, and at last pay all the debts as well. It seems to me hard that he should pay in life and money both.’” (B.1, ch.35) 

Amy is no longer a saint. 
In the 2nd half of Little Dorrit, Dickens lets the reader enter her mind, and she therefore becomes more like a person. She has an inner world. 

 “Sitting opposite her father in the travelling-carriage, and recalling the old Marshalsea room, her present existence was a dream. All that she saw was new and wonderful, but it was not real; it seemed to her as if those visions of mountains and picturesque countries might melt away at any moment, and the carriage, turning some abrupt corner, bring up with a jolt at the old Marshalsea gate.
To have no work to do was strange, but not half so strange as having glided into a corner where she had no one to think for, nothing to plan and contrive, no cares of others to load herself with. Strange as that was, it was far stranger yet to find a space between herself and her father, where others occupied themselves in taking care of him, and where she was never expected to be. […]
It was from this position that all she saw appeared unreal; the more surprising the scenes, the more they resembled the unreality of her own inner life as she went through its vacant places all day long. The gorges of the Simplon, its enormous depths and thundering waterfalls, the wonderful road, the points of danger where a loose wheel or a faltering horse would have been destruction, the descent into Italy, the opening of that beautiful land as the rugged mountain-chasm widened and let them out from a gloomy and dark imprisonment—all a dream—only the old mean Marshalsea a reality. Nay, even the old mean Marshalsea was shaken to its foundations when she pictured it without her father. She could scarcely believe that the prisoners were still lingering in the close yard, that the mean rooms were still every one tenanted, and that the turnkey still stood in the Lodge letting people in and out, all just as she well knew it to be.
With a remembrance of her father’s old life in prison hanging about her like the burden of a sorrowful tune, Little Dorrit would wake from a dream of her birth-place into a whole day’s dream...” (B.2, ch.3) 

These passages are the counterargument if anybody says Dickens is not a serious artist and cannot write well-rounded characters. 
If in Book 1, Dickens writes about Amy mostly from the outside or from the perspective of Arthur Clennam, in Book 2, he writes a lot more about her thoughts, perceptions, and feelings. The change in the Dorrit family’s fortune and their new life are chiefly seen through her eyes. 

“She would watch the sunset, in its long low lines of purple and red, and its burning flush high up into the sky: so glowing on the buildings, and so lightening their structure, that it made them look as if their strong walls were transparent, and they shone from within. She would watch those glories expire; and then, after looking at the black gondolas underneath, taking guests to music and dancing, would raise her eyes to the shining stars. Was there no party of her own, in other times, on which the stars had shone? To think of that old gate now!
She would think of that old gate, and of herself sitting at it in the dead of the night, pillowing Maggy’s head; and of other places and of other scenes associated with those different times. And then she would lean upon her balcony, and look over at the water, as though they all lay underneath it. When she got to that, she would musingly watch its running, as if, in the general vision, it might run dry, and show her the prison again, and herself, and the old room, and the old inmates, and the old visitors: all lasting realities that had never changed.” (ibid.) 

Not only so, Dickens lets Amy speak: chapter 4 is her letter to Arthur. The letter contains some self-depreciation, and kind words about other people, as one would expect from Amy. But look at this: 

 “It will not make you uneasy on Mrs Gowan’s account, I hope—for I remember that you said you had the interest of a true friend in her—if I tell you that I wish she could have married some one better suited to her. Mr Gowan seems fond of her, and of course she is very fond of him, but I thought he was not earnest enough—I don’t mean in that respect—I mean in anything. I could not keep it out of my mind that if I was Mrs Gowan (what a change that would be, and how I must alter to become like her!) I should feel that I was rather lonely and lost, for the want of some one who was steadfast and firm in purpose. I even thought she felt this want a little, almost without knowing it. But mind you are not made uneasy by this, for she was ‘very well and very happy.’ And she looked most beautiful.” (B.2, ch.4) 

She sees through Henry Gowan. If the reader has been under the impression that, in her passivity and self-sacrifices, Amy is naïve and believes everyone to be better than they are, they are mistaken. She sees through Henry, and in expressing it to someone else (Arthur), she becomes more human.  
Amy also sees through her own father: 

“Little Dorrit, whether speaking or silent, had preserved her quiet earnestness and her loving look. It had not been clouded, except for a passing moment, until now. But now that she was left alone with him the fingers of her lightly folded hands were agitated, and there was repressed emotion in her face.
Not for herself. She might feel a little wounded, but her care was not for herself. Her thoughts still turned, as they always had turned, to him. A faint misgiving, which had hung about her since their accession to fortune, that even now she could never see him as he used to be before the prison days, had gradually begun to assume form in her mind. She felt that, in what he had just now said to her and in his whole bearing towards her, there was the well-known shadow of the Marshalsea wall. It took a new shape, but it was the old sad shadow. She began with sorrowful unwillingness to acknowledge to herself that she was not strong enough to keep off the fear that no space in the life of man could overcome that quarter of a century behind the prison bars. She had no blame to bestow upon him, therefore: nothing to reproach him with, no emotions in her faithful heart but great compassion and unbounded tenderness.” (B.2, ch.5) 

That is such a wonderful passage. 
Now look at this: 

“In such further communication as passed among them before the sisters took their departure, Little Dorrit fancied it was revealed to her that Mr Gowan treated his wife, even in his very fondness, too much like a beautiful child. He seemed so unsuspicious of the depths of feeling which she knew must lie below that surface, that she doubted if there could be any such depths in himself. She wondered whether his want of earnestness might be the natural result of his want of such qualities, and whether it was with people as with ships, that, in too shallow and rocky waters, their anchors had no hold, and they drifted anywhere.” (B.2, ch.6) 

Another wonderful passage. It’s almost like something out of a Jane Austen novel. 
It shows Amy’s sensitivity and perceptiveness, and at the same time, also suggests that in this regard, Arthur isn’t much better than Henry either.