One of the things I liked about her solo series was when she set up a practice under a fake name and showed she was actually a competant psychotherapist.
Even though people in numerous places implied she didn't earn the grades, she just seduced the professors into giving her high marks (the Mad Love comic and at the beginning of Harley's solo for example).
Personally I think that she'd have gotten high grades anyway, but the low self-image that caused her to fall for the Joker's flattery caused her to feel that she cheat to get the grades she'd have gotten anyway.