I don’t think Darcy’s comment in Ch. 32 or question in Ch. 33 of P&P proves Emma did not ask Jane questions that were impertinent. Like Emma, Darcy has an agenda to take into account. IMO he is not making idle conservation rather he is considering proposing to Lizzy and brings up the Collins marriage because he wants to know her ideas on marriage—if they are compatible with his opinions. He also believes Lizzy knows what he is about and at times is more familiar with her than normal. In Ch. 32 Darcy says “Mr. Collins appears very fortunate in his choice of a wife” which is not a question. I feel Lizzy’s response reveals her struggles accepting the marriage and is primarily a voluntary defense of why her friend is happy with a silly pompous toady of a man:

"Yes, indeed; his friends may well rejoice in his having met with one of the very few sensible women who would have accepted him, or have made him happy if they had. My friend has an excellent understanding -- though I am not certain that I consider her marrying Mr. Collins as the wisest thing she ever did. She seems perfectly happy, however, and in a prudential light it is certainly a very good match for her." (P&P, 32)

Although it is the truth and worded amusingly I think Lizzy speaks too freely of her friends to a man she does not like or respect as a person. She makes sport of Mr. Collins and admits to questioning Charlotte’s judgment in her choice. Also Lizzy thought Darcy’s asking “her opinion of Mr. and Mrs. Collins's happiness” (P&P, 33) to be odd. I agree it is perfectly reasonable to chat about the wedding of an acquaintance but the Dixons do not appear to be of Emma’s acquaintance and she has no reason to suppose after years of neglect on her part that she and Jane are in any degree intimate. Asking Jane her “opinion of the suitableness of the [Dixon’s] match” (20), probing for details of the Dixons relationship to verify her suspicions, seems to me impertinent.

Emma, by virtue of her situation, outranks Jane and by her own admission has neglected her socially so it is not just Mr. Knightley’s idea that she had been “unjust to Jane” (21) in the past:

“ Emma was sorry to have to pay civilities to a person she did not like…to be always doing more than she wished, and less than she ought!” (20)

I don’t think Mr. Knightley is trying to force Emma, against her inclination, to like Jane or overcome her diffidence. He saw Emma’s proper attention to Jane the night previous and expressed his “his approbation of the whole… great pleasure in marking an improvement” (21). Her behavior suggested to him that she wants to treat Jane with the proper attentions and befriend her. Emma might have set Mr. Knightley right if she wished but she did not because she wanted to please him:

"My dear Emma," said he, moving from his chair into one close by her, "you are not going to tell me, I hope, that you had not a pleasant evening."

"Oh! no; I was pleased with my own perseverance in asking questions, and amused to think how little information I obtained."

"I am disappointed," was his only answer.

…Emma saw his anxiety, and wishing to appease it, at least for the present… (21)

At this point I don’t think Mr. Knightley deserves any censure on this subject—he does not think he is trying to force Emma into a relationship she does not want. Perhaps if she had confessed her real feelings about Jane Fairfax instead of “She is a sort of elegant creature that one cannot keep one's eyes from. I am always watching her to admire; and I do pity her from my heart” (21) Mr. Knightley’s ideas, advice, approbation and gratification wound not be so off the mark.