I don't subscribe to the idea that drug use makes someone a bad person and I am pro legalisation of drugs and prostitution so there's that
More than that, I am willing to believe that Quinn may, and that's the key word in this sentence, have initially got into this as an easier way to fund the sorority than the standard work they do and quickly found it to be lucrative enough that it could be used to fund the tuition fees of the restaurant staff.
Her behaviour at this point may (there's that word again) be a result of too many pledges wanting the free tuition without knowing what's required to earn it (and clearly not being the sort of girls who would be doing it free, unlike Sarah, Mel and Camilla)
I still believe she's made her bed and has to lie in it but I can also understand how she got into this situation.