She was probably concerned about medical or daycare assistance. Cash and food phase out so you never lose more than you've gained in earnings, but medical has hard cutoffs and I believe childcare does as well. I've known a few families in that position with health coverage over the years, where a raise or promotion would actually cost them hundreds of dollars a month plus hundreds more in deductibles throughout the year because it put them over the cutoff and their employer-sponsored insurance cost much, much more than the new wage added to their bottom line. Or worse, the raise put them over the cutoff but the job didn't offer benefits. In some cases, it might make sense to limit oneself for a period of time (until those kids start school, for example, so the money being spent on daycare can be used for insurance premiums instead).