"She was wrong.
He was wrong.
She made an inappropriate sexual comment about his promiscuity.
He made an inappropriate sexual gesture at her."
@sailorcherries - whilst I agree with you that two wrongs do not make a right, I think this part of your post shows a bias towards the boy. By putting the girl's actions ahead of the boy's, you give the impression that she was the instigator in this incident, and that the boy's words and actions were in response to the girl's, when in fact the opposite is true. He was the aggressor, the sexual harasser, she was the victim of sexual harassment.
By writing the post as you did, you give the impression of bias towards the boy in this incident - that is based purely on this post.
It is very easy for people to criticise the girl's response as being OTT, but in my opinion she reacted in the moment to an unpleasant incident of sexual harassment - she did not have the luxury of being able to consider her response, in an atmosphere where she did not feel under threat.
She will probably have been experiencing the 'fight or flight' response - she reacted instinctively and chose fight.
I am also a little surprised that some people seem to think she should have reacted politely to being sexually harassed - I find that mind boggling, and not in a good way!