The slayer association isn't any big deal to me; my issue is with the nicknamey-ness. I've always thought a really nickname-sounding name ought to have a full, or more formal, given name so the individual has the option to use it. That said, I would never assume a woman named "
Buffy" couldn't be a doctor or anything else she wants to be. Personally, I wouldn't choose
Buffy as a nickname but I don't see anything wrong with it.