In P&P Lizzy “felt all the impertinence of her [Lady Catherine’s] questions, but answered them very composedly” (29). Here is the description of the questions Lizzy thought impertinent:

[Lady Catherine] addressed a variety of questions to Maria and Elizabeth, but especially to the latter, of whose connexions she knew the least… She asked her, at different times, how many sisters she had, whether they were older or younger than herself, whether any of them were likely to be married, whether they were handsome, where they had been educated, what carriage her father kept, and what had been her mother's maiden name? Elizabeth felt all the impertinence of her questions, but answered them very composedly. (P&P, 29)

If Lizzy is correct in believing these questions are impertinent, and I have never seen anyone argue that they are not, then to my mind Emma’s questions about the Dixons and their marriage are also impertinent. For example Lady Catherine only asked if any of Lizzy’s sisters were likely to be married but Emma asks Jane her “opinion of the suitableness of the [Dixon’s] match” (20). Also it seems to me Jane’s interactions with Mrs. Elton and Mr. John Knightley in Ch. 34 suggest her disgusting suspicious reserve about the Dixons, Weymouth and Frank Churchill (20) is greater than what is seen as her normal reserve.