It all depends who she is and where she came from,i assume her name is not in the house
book or rental agreement?
In that case she has no reason to be there.
Just make very sure you do not get into a screaming match,and never in front of the police.
Let them see first hand how crazy she is,i would not worry too much if i were you.
In a similar case i saw a senior police man ask the woman where she came from and he told her very impolitely to go back there in a hurry or he would lock her up,she left.