Readers learn about Daisy's state of mind in a memory that Jordan shares with Nick.
Apparently, Daisy received a letter from Jay Gatsby on the eve of her wedding to Tom Buchanan. Readers do not know the content of the letter, but it is reasonable to assume it is a love letter, and perhaps he is asking her to continue to wait for him.
Daisy becomes tearful and drunk and ends up in the bathtub of her family's home, unwilling to let go of the letter. She takes the very expensive pearl necklace Tom gave her and tells Jordan and the other women present to return it to Tom, along with the news that she has changed her mind about marrying him.
It seems Daisy is very conflicted about marrying Tom because she still has feelings for Jay Gatsby.