Pride and Prejudice Volume 3, Chapter 15
Elizabeth is stressed over Lady De Bourgh's visit because she knows that the woman will speak to Darcy on the topic, which will only embarrass Elizabeth further. Elizabeth also isn't sure how much Lady De Bourgh's opinion matters to her nephew, but Elizabeth worries that if LBD lists all Elizabeth's disadvantages to Darcy the way she did to Elizabeth herself, any affection that Darcy still has for Elizabeth will be destroyed. But more disturbing than all of that is that she doesn't know where the rumor started. She guesses that the excitement over Jane's engagement naturally matches Elizabeth, Jane's sister, to Darcy, the groom-to-be's best friend. She bets that the Lucases made some such prediction in their correspondence to the Collinses and that's how Lady De Bourgh found out.
Elizabeth's suspicion is confirmed when her father calls her into his study to hear the latest letter from Collins which congratulates him on Elizabeth's engagement to Darcy. Mr. Bennet is amused that anyone could ever imagine a match between someone as wealthy as Darcy and Elizabeth who hates Darcy so much. Elizabeth endures the pain of her father's amusement and thinks that perhaps he's right that her own desire to regain Darcy's affections has made her imagine any affection between them.