... I sent the previous message prematurely, before addressing the rest of your message.

I've just addressed your idea that Emma was self-judging.

I don’t see this happening in childhood when Jane had yet to become proficient.

Jane left for the Campbells before she was 9. Most of their lives has been spent apart (ch. 20). There's not the least evidence that they were ever friends, and plenty of evidence of Emma's longstanding dislike and jealousy.

Here Jane’s thoughts would be useful. Did she feel superior as a ‘city’ girl during her visits? Did she feel envious too of Emma’s situation in life, while growing up?

True enough. Emma, however, accuses her of being "reserved" and "cold" even before she returns to Highbury (ch. 20). More below.

The bolded letters are all Emma's thoughts, and seem to me like expressing resentment or regrets about things of adulthood.

What you see as Emma's thoughts I see as the narrator describing Emma's attitudes, with no qualification at all about recent times.

I for one cannot imagine a very passive Jane who had no negative thoughts or resentments even while growing up during those short visits if we are to suppose Emma had.

Nor can I. Thus, I ascribe most if not all of Jane's reserve to prudence due to, or maybe resentment of, Emma's treatment of her. And since I don't accept the idea that Emma is self-critical, I see Emma's guilty conscience as evidence of treatment even worse, probably, than Emma acknowledges to herself (assuming the bold quotes are her thoughts).