@Wendz,
GG thinks this is a romantic situation between two girls!!! My thinking.
My advice,
These situations will never resolve unless very firm action is taken. One has to be ready to involve the police and get her arrested for trespass. I am not sure whether you can get a prohibition order from the courts so that the person is jailed should they ever set foot in your property ever again - lawyers please advise.
The downside is that you may be arrested for battery and charged, but if you can prove self defense.. Again lawyers in the house should assist.
My two cents.
Great men are not always wise, neither do the aged understand judgement...