The subtitle of Nickel and Dimed is On (Not) Getting By in America. It is important to note how Ehrenreich chose to put "not" in parentheses, and that choice on her part is directly related to her primary theme which is that it is virtually impossible to provide basic needs for one's self by working one minimum wage job. While the reality is that most minimum wage workers are forced into working more than one job to make ends meet, Ehnrenreich's philosophy is that if the government sets a "minimum" wage, shouldn't that wage at least be enough for someone to provide his or her basic necessities?
For the author, her most significant moral dilemma seems to be when she works for a housekeeping company as a maid. She finds herself pondering what makes it okay or moral in America--the land of opportunity--for one person to have so much that he or she pays another person (who is supposed to be equal) to scrub one's toilet. She also struggles when one of her coworkers (from "Scrubbing in Maine") is malnourished and obviously weak yet refuses to get help. Ehrenreich believes that it is not her coworker's choice to keep plodding painfully through life but that she has an obligation to do something about her coworker's plight. She stresses this idea through other examples in the book.
One thing to be careful of when reading Ehrenreich's book is that she has an agenda when she sets out on her "experiment"; so you have to weigh her objectivity cautiously. An interesting counterargument to Ehrenreich's book and themes is Adam Shepherd's Scratch Beginnings: Me, $25, and the Search for the American Dream. He, too, has an agenda--to prove Ehrenreich wrong; so it is good to read both and then to decide which you think is a more realistic portrayal of life in minimum-wage America.