some women i've trained with have not been socialized at an earlier age to have a lot of tolerance for contact. my friend who leads classes in choy li fut says that females in his beginning class have a hard time sparring with men (esp the beginner men who hit hard) and tend to drop out easily. the ones that make it to advanced level do fine. being supportive while they become more accustomed to the nature of traditional martial arts training will help with retention.
as for the note about women being able to hit hard but not being able to be hit hard, i've seen that too (with a few exceptions). i think it's largely psychological. it would be of benefit for more women to develop that resiliency (and anyone for that matter, no matter what size).