I had to rush away. To continue;

The quotes from Ch:12 and CH:19 are hilarious. They do divert me against my conscience. They are a hoot, especially when I picture the scene. :-D

>I can well understand his bitter disappointment at seeing his wishful thinking on Emma's good will quashed by Emma herself.

Well, Mr Knightley has to learn a lesson or two too, IMO :) .
His thinking is so one dimensional, so assured that he is right, while not knowing a thing about the interaction...'and' feelings from both sides.

If I were Mr Knightley I would ask Emma for the reasons of her so called, by him 'neglect'.

>It was a dislike so little just -- every imputed fault was so magnified by fancy, that she never saw Jane Fairfax the first time after any considerable absence, without feeling that she had injured her; ... These were charming feelings, but not lasting. Before she had committed herself by any public profession ... every thing was relapsing much into its usual state.... She [Jane] was disgustingly, was suspiciously reserved.

That's typical Emmaish behaviour.
She always judges herself severely at first only to let her chagrine dissove her resolve - and we have her reason here.

If it's Jane's right to answer vaguely without giving any information, I think it is only normal not to feel very friendly with someone who gives such a response.