I'd make all my decisions in there interest of protecting the child involved. She's obviously been in several inappropriate situations, who is watching her and guarding her so this kind of thing does not keep happening to her? I had a friend who was being molested by her uncle when we were children. I didn't learn the facts until we were adults. What I remember about her behavior back then was that she seemed really boy-crazy at a very young age, and dying to grow up fast. She'd see some guys older than ourselves when were downtown and say, "Let's follow those boys." Stuff like that, which in a preteen would possibly be written off as trying to grow up fast, but in a younger child should be a warning sign. How is she even getting into a situation where someone could show her a private part at school and ask her to put it in their mouth? Who is telling her to be this compliant?
I guess if you feel an adult in her life is suspect, you need to report things to authorities. If you feel the adults in her life would be concerned and want to protect her, you need to tell them. If you feel she would just get into more trouble if you said anything, I would talk to a minister or counselor to help you find the right path. But the child deserves to be safe and grow up in a non-sexualized environment.
Totally agree with Annie a red flag goes up here this child needs protecting make sure you are aware of anything in your house ,..eyes wide open Mom supervision and protection required ..