Daisy tells Nick that she is "cynical about everything". She bemoans the idea she expresses about her own sophistication and she tells Nick that she hopes her daughter will grow up to be a fool.
Daisy's unhappiness is at the forefront of her talk with Nick and he feels that she is performing an act for him meant to elicit a particular emotional response from him. Nick finds that her speech leaves him feeling the "basic insincerity" of everything she has said, about her daughter, her cynicism and her sophistication.
Daisy's unhappiness must be seen with some suspicion at this point, given Nick's response to the act that Daisy has put on for him. Though her husband is cheating on her (and this is the subject of dinner conversation), her emotional state must be seen as being complicated by false appearances, eagerness to perform, and a quality in her voice that suggests a variety of motives (one being to express allure and to captivate).