My Girlfriend's Ex is Threatening Her (With a Twist)?

Okay so my girlfriend had a bad breakup with her ex. He threatened to kill her and her family over text and continues to say that he is going to "get" her. Here is the twist, she slashed his tires and was sent to jail for a few hours in a reaction to his texts and treatment of her. She seems convinced that the police won't do anything for her because she vandalized his car.

I'm not trying to justify her behavior, but he has apparently put his hands on her before. What should she do?