The major thing to remember is.. It's HER choice to do drugs, or to get help. Soo don't feel that it's somehow your fault, that you aren't doing enough to help her etc. I'm not saying don't try to help her, but if you offer help every single day, and she turns it down every single day, don't feel as if its all your fault. The guilt will do nothing but tear you down.
I'd second the get her snatched up while high to be taken in. But if she doens't want to quit, she won't quit. End of story. No one can Make her want to quit. You can talk to her, and BE BLUNT. Tell her "Honey, I'm afraid I'll find you dead one day. That would really just kill me inside. You should really quit for YOU."
Anything you want to try that's legal, try it.. the alternative is her OD-ing and/or ruining her life in the mydrid other ways available to a drug addict.
HUGS to you, and remember no matter what happens, it isn't YOUR choice that she is doing drugs. Keep yourself as strong as possible to better be able to help her. In fact, you could look into counciling for yourself as well.
Wolfy