Superficially, it might appear that Daisy cries about Gatsby's "beautiful shirts" purely because she is a woman who appreciates money and material things. This is, after all, the overriding impression she exudes: she has a voice "full of money" and seems driven to associate with people who can provide her with beautiful things. Gatsby knows how much she loves beautiful things: he is revaluing everything in his house, Nick says, depending on how Daisy reacts to it.
However, there also seems to be another element at play here. When Daisy knew Gatsby and loved Gatsby, he was not the sort of man who could ever have afforded shirts of this quality. Daisy sobs over the shirts, then, partly because they are beautiful, but also surely in part because she is both proud and devastated to know what sort of man Gatsby has become. As he is now a wealthy man, she could have married him and had not only his wealth, but his love. She is glad for Gatsby that he is able to afford these things, because she does love him. At the same time, she is crying about the life she set aside because, at the time, it did not fit with what she expected and what was expected for her. If only Gatsby had been able to afford such beautiful shirts earlier in their acquaintance, she would not have married Tom and would have been much happier today.