Girl forcefully written application to marry her, please advise

Sir,my elder brother in relationship with girl since 2 year and but girl is cheater bcz she strated blaickmailling and forcefully wants to marry him but my brother doesn't want to marry her and she having some picture along with my brother and some vedio too but that vedio my brother nothing doing anything wrong.but she complaints in police station and forcefully written application to marry her and my brother have to written.And the big mistake is we don't known anything about her.we dont knows where is her village bcz she working in b.p.o in city and her parents live in village and she doesn't want to contact her parents.one thing I tell she did already fraud case to some another boy but that boy was clever he have left city.and my brother working in good position that's why she made plan and my brother stuck that plan.sir what should we do.