How long has she been masturbating? How did you find out about the masturbation? And how did you find out about the bruises?
Her legs rubbing together as she walks should not cause bruising at all. Normal masturbation should not cause bruising to her thighs. I would definitely, and quickly, check into possible abuse - it's really the most logical cause of the bruising.
she could have a pain fetish and abused herself OR experimented to c
I agree with myenzoorka !!! Yesterday is not soon enough to get that child to a doctor and have her checked out.