Morality and ethics
Although Tess makes bad decisions, she is continually growing and becoming more honest and active in her own life. She sacrifices moral goodness as an ethical experiment to gain experience. By ignoring the safety that morality provides, she does darken her fate by introducing binge drinking and sexual indiscretion to her life, but she also progresses in her journey toward wholeness. The point is that by judging her behavior, the reader would miss the ethical progress of her character.
Nepotism
Tess is up against the incestuous relationships of Jake and Simone, and also of the restaurant to its employees. Because waitressing in New York is a taste of the night life, there are cliques at work like there would be at parties, and although Tess never realizes what it is about the situation that she despises, it is nepotism, the priority of one's own people over others.
Anonymity and community
This is what New York City represents in the American zeitgeist, and this novel is no different. Tess goes to New York to be around new people, to be overwhelmed by different people's points of views, and to be changed by them. But is the anonymity of New York what she really wants? No, she clearly wants to establish a community, but ironically, the density and population of New York City don't really accommodate her emotional needs.
