M.B.
Unfortunately, with her being 18 now, you cannot mandate her attending a help group or something like that without a court order.
I would look into filing an eviciton notice and/or a restraining order against her.... that way, if she does come back, they can legally pick her up and maybe that would get the legal wheels rolling to get her some court-mandated help.
I'm sorry you've had to deal with this...... there are some teens, because of the many problems they may have (I'm not saying you caused them..... some kids, because of the choices they've made, have messed up their minds big time with drugs and alcohol), that they are no longer safe to be around.
Is there a social worker that can help you through this minefield? Good luck with all of that......