All your points are valid OP. It might make matters worse to call the police.

1. try noise--say something licked in the tunk or under the hood that makes enough icky noise that someone could not sleep in there.

2. find her somewhere else to sleep.

There is nothing that will bring good Karma into your life like helping those who seem unloveable. This woman has probably been abused since she was a child, she is probably very broken and hurting--the drugs are the only way she knows of stopping the pain.

Spiritually it would seem she has come into your life for a reason--this is a test.

If you don't wish to help her, I understand, at least you don't want to harm her, the noise should work--some kind of repetitive alarm or beeping noise, or for halloween something scary, haunting....

Good luck!!