Hello lostinlove1973 and

to Psych Central,
Getting off methadone (and other drugs) isn't easy at all. In my opinion, the key is actually being ready to commit to getting off the drug. If your gf isn't ready ~ and if she isn't real willing to go through the withdrawals, chances are very slim that she can do it.
I can understand your fear of your girl meeting and connecting with another guy while in treatment. I'd would recommend that you visit her regularly, showing your support at every visit. She'll learn that you're always there for her. That will be very reassurring to her. Do know that people in rehab can be very angry and mean during detox. It does hurt!! If your gf does this to you during a visit, tell her that it does hurt & leave. As the detox goes on, she should become more kind and appreciative of your support and love.
It takes time. Don't give in to emotional outbursts & lose it. Just back off a bit ~ and keep going to show that you do care. Best wishes to you both!