You have no lease agreement, verbal or written..she is an overnight guest who has overstayed her/his welcome, it could be 5 years, doesn't matter. Mail doesn't matter.. Cops will tell you differently if she calls them but they are wrong, stick to the she's an overnight guest who has overstayed her welcome story. You could have them call your lawyer when they disagree with you and you don't have to open the door for her or the cops if she shows up with them. You can leave her stuff somewhere locked up safe like the garage and change the locks before she gets home. Now, if she paid rent and can prove it, not utilities, you're screwed and must evict.