It really bites when you try to help someone, then you find out that they don't want to help themselves.
Id push her car to the curb, when she shows up again give her the keys and have all her stuff in garbage bags waiting for her.
Sanitize everything she has touched. If she is "dating" she most definitely stands a good chance of having hepatitis a,b,c,d,e and of course any other type of STD.