Daisy's comment about her little girl appears near the end of Chapter 1. She tells Nick,
" 'Well, she [Daisy's baby] was less than an hour old and Tom was God knows where. I woke up out of the ether with an utterly abandoned feeling, and asked the nurse right away if it was a boy or a girl. She told me it was a girl, and so I turned my head away and wept. ‘all right,’ I said, ‘I’m glad it’s a girl. And I hope she’ll be a fool—that’s the best thing a girl can be in this world, a beautiful little fool.'"
This comment is another part of the awkward conversation between Nick and his cousin during the Buchanans' dinner party in Chapter 1. Nick had brought up the subject of Daisy's little girl to try to get Daisy's mind (and the conversation) off of Tom's mistress who was calling.
Daisy's feelings about the birth of her little girl also foreshadow her affair with Gatsby. Not only does she reveal in her quote, that Tom's cheating is nothing new to her, but she also relays her loneliness and need for someone to idolize her.
Daisy's comments about the birth of her daughter reveal the situation of women in society at this time. There is nothing for a girl to do but be pretty and stupid. That is the only accpeted role for a woman; if she wants to go anywhere in society, she can't be intelligent or independent -- only stupidly compliant. Re-read the passage about Daisy's wedding -- you'll see that portrait of compliance there, as her mother forces her to marry against her will.