If he defends himself against her, she can always say he
"molested" her. He will then be caned on the anus. Next, he will go
to a boys' home, where guards and 17-year-old boys [who are the
dominant inmates] will torture, degrade, beat, and do things to him
that are not appropriate for discussion.
BTW, boys homes smell terrible, like sweat, vomit, and
excrement.
If this boy [who is only 15] goes to this home for "molesting" a
girl, the guards and the 17-year-old boys will make him smell bad,
smell him, and then insult him about how he stinks.
So my best advice for this boy is, let the girl do what she
wants to you. Better to be harassed by a girl than by men and
bigger boys.