her parents know about it, so stay out of it.
It's up to them to step in, not you.
When I was 20, I hung out with my boss's 16 year old son (we were both interning at the company).
He was a cool kid and really mature for his age.
Fun to hang with.
I don't deny that I was attracted to him, but I respected the age difference and made sure I kept things at a friendship level, nothing more.