He is going to have to be firm. Tell her once and for all that he is not going to be in her life. Yes, she probably will act out but that is her choice not his. He cannot be responsible for her actions unless he wishes to be in this relationship until her eventual death. I would suggest that he talk to her mom one more time. She doesn't like him so he can start out with "I know you don't like me so I want to do you a favor and get out of your daughters life. I will not see or talk to her again. I am afraid that she may do something that will endanger her so please keep an eye on her." Then he has to move on. If she continues to follow him around he can get a restraining order on her.

I hate giving advice like this because I have a fairly good idea how she is feeling and it is not good. Her pain is running deep, she needs help. But there comes a time when a person continues to refuse to help themselves that the people around them need to get on with their own lives. I sincerely hope she gets the help she needs.
Carrie

<font color=green>Not knowing when the dawn will come, I open every door.--Emily Dickenson