Because it is a journalistic account of her experiences, Barbara Ehrenreich does not use many metaphors in Nickel and Dimed. The book's literary style is personal and intimate, rather than dry and scientific, but it still is a fairly simple event-by-event account. The few examples of metaphor occur serve mostly to underline the hardship of working minimum wage.
Early in the book, Ehrenreich comments:
The whole thing would be a lot easier if I could just skate through it like Lily Tomlin in one of her waitress skits... After a few days at Hearthside, I feel the service ethic kick in like a shot of oxytocin, the nurturance hormone.
(Ehrenreich, Nickel and Dimed, Google Books)
Lily Tomlin used her waitress experience to perform comedy routines, and since these are played for laughs, the experience itself seems easier. Ehrenreich's real-life waitressing is much harder and requires a great deal of concentration and focus; she cannot "skate through it" by doing the bare minimum. Comparing the "service ethic" to oxytocin, which is a hormone indicated in maternal behavior, is both a reference to her gender -- women secrete more oxytocin in men -- and to pride in her job. She mentions her father, who raised his family from the copper mines and taught her to overachieve; in this case, as if artificially injected to care about the job. The necessity of working well and earning money is stronger than her dislike of the job.