Originally Posted by ScottGem
The police will not help you, but it won't hurt to call them. But I would not take legal advice from a policeman. The problem is this is a civil issue, not a criminal one. Unless it becomes criminal the police don't get involved. The only reason to call the police is if she gets physically abusive. Then you call them immediately.
Who you really need to consult is a real estate attorney. I totally and completely beleive that you need to go through a formal eviction. Anything less will potentially open you up for trouble.
You didn't answer some of the speculation here. You are renting, correct? And does your lease permit sublets or roomers? Did you give her a receipt for what she has paid? Does she get mail at the residence?