Its been a while since I've read Ehrenreich's book but am curious - which decisions of hers did you find irrational?
I will say that a fundamental flaw in Nickel and Dimed, (and most likely in Shepard's book as well) - is that she ultimately had a choice. Many people in these situations have no choice. Many of them have children. Many of them have no college education to fall back on. I count myself among the lucky.