oh wow! you are in one tough situation.
If it was me in the situation...I wouldnt want to get involved. You nvr know if this bhabi is telling the truth or not. She is a grown woman and should be able to handle her own. If she cant....then advise her to talk to her father or brother. They should be the ones to set him straight....not you.
P.S she should hit him back :D
^ its funny that you are saying she is a grown woman and should be able to handle her own problems, but in another post you said "should" isn't always the case. at least she is reaching out and not just keeping the problem to her self.