I've been in a similar situation as your daughter. Not with a meth addict, but a prescription drug addict and general creep. I was with him through my entire early twenties. I loved him, but I also hated him. I wanted to leave, but I coukd never pull the trigger because he would never do anything concretely horrible that I could put my finger on (never overtly caught him cheating, he never physically abused me), and I worried I'd never find someone else. Looking back, it's clear that he had systematically destroyed my self esteem for this very effect. My dad went in circles trying to help. It wasn't until i finally caught him stealing from me that I broke it off for good. I'd hated him for years, but I was trapped.
Here is my advice:
Be the safe place she can come to. Don't give her a hard time. Tell her you think she deserves better and you worry for her, but make sure she doesn't start pulling away from you. He's isolated her from her support (her friends don't come around anymore, remember?). It's REALLY, really hard to leave a bad situation if you don't have a support network. Make sure you are that.
Get her on birth control if she's not already. My parents and I never really talked about it, but that shit just appeared on my dresser one day. Lol. Looking back, I'm soooo thankful for this. Getting tied to that bastard for life by a child would have been a disaster.
3.Get here out and experiencing the world as much as possible. Can you afford to send her and a friend to Europe for a backpacking trip? The plane tickets would be by far the most expensive part. Travel within Europe is dirt cheap, and getting the loser out of your lives will save you money in the long run, trust me. If you can't send her across an ocean, have her mom take her on a trip. Don't let her go by herself domestically; its be too easy to have the dirtbag meet up with her.
This is a shit situation, and I'm so sorry you're dealing with it. Now that I'm a mom, I feel terrible for putting my parents through such worry. If you wanna talk more, let me know.