Op, if your daughter does do this, please help her understand how vulnerable she is if she sleeps on the plane. Make sure she tucks the blanket right around her, think about how accessible her clothes make her etc and before everyone jumps in, yes I know she shouldn't have to.
I fly very frequently with work long haul, and have witnessed some terrible things and also been targeted quite a few times. Even though we only fly business or above where it's more open and obvious, it still happens.
The only times it doesn't happen is when I'm flying with my DH, boss or dad, so i haf not really noticed it was a thing till i started flying alone a lot around 10 years ago. My views have now changed a lot.
The cabin crew are helpful and know it happens, openly acknowledging it when you point it out but by then it's too late.
Not trying to scare, but it's something I simply wasn't aware of as a danger and was pretty scared and tearful the first time I felt a wandering hand.