How To Find Your Friend Is In Trap.............

That seems like a big problem. Nothing can actually be told about the solution unless we know how your friend was trapped. If at all there is any legitimate proof of the so called sexual harassment that your friend committed then it can be difficult.
If there is no such proof then find more of her victims and discuss with each other and analyze her behavior and weaknesses. Propose a plan to trap her. Even if you get an iota of proof which proves her as debauched, take help from the media and spread it like wildfire. That may open some more doors.
Analyze the situation like a math problem. But most importantly ask your friend never to lose hope as such things keep happening and people are gonna try to take advantage of you and pull you down but don't resort to any form of violence.
"It's not how hard you can hit, it's how hard you can get hit and keep moving forward"-