How does Daisy behave the night before her wedding? Why?

Daisy got roaring drunk and cried over a letter that she'd received from Gatsby.

I was bridesmaid. I came into her room half an hour before the bridal dinner, and found her lying on her bed as lovely as the June night in her flowered dress — and as drunk as a monkey. She had a bottle of Sauterne in one hand and a letter in the other.

She began to cry — she cried and cried. I rushed out and found her mother’s maid, and we locked the door and got her into a cold bath. She wouldn’t let go of the letter. She took it into the tub with her and squeezed it up into a wet ball, and only let me leave it in the soap-dish when she saw that it was coming to pieces like snow.

But she didn’t say another word.