Character Analysis
We don't learn a whole lot about Daisy, apart from the fact that Moses Herzog treated her terribly during their marriage. If anything, the pain Herzog caused Daisy helps justify Madeleine's horrible treatment of Moses during his second go-around on the matrimony carousel. Herzog has virtually nothing to do with Daisy, but he still needs to see her when he visits his son Marco.
He dreads visiting Marco because he knows he'll run into Daisy, who is (for good reason) never happy to see him. As he imagines at one point,
Daisy would try to be stolid. It did great harm to her looks. She met Moses at the top of the stairs, her arms crossed, turning herself into a square figure with green eyes and chopped hair, waiting to say he must bring Marco home within two hours. (4.3)
Herzog is a dude who gets through awkward moments by using humor. But this technique never works with Daisy because "She had good qualities, but a sense of humor was not among them" (4.3).
Ultimately, Daisy is in this book to remind us that we shouldn't feel too bad for Moses after Madeleine leaves him. After all, he hasn't been a saint in his love life; he's hurt more than a few women along the way.