Most Helpful Girl
I think at some point everyone is responsible for their own life. Your girlfriend has made up her mind. She has chosen to be a drug addict. You are not responsible for her and her decisions. Don't ruin your life because of her. She needs to figure out things on her own. You can't make her quit. She needs to want it herself. You can't help someone who doesn't want help.
The best thing you can do is to tell her about your feelings and make it clear to her you are fed up with the situation. You have given her every chance but it's over.
You need to live your life. Don't ruin it for someone as selfish as her. Don't feel bad. She has parents. I don't believe anyone loves you more than your mom, so if her mom has given up on her you can't change her.
Most Helpful Guy
Kick her out. You've probably already thought about all the points I'm going to make, but I'll make them anyway.
1) It might seem cruel to her, but continuing with the status quo is cruel to you also. There is a point where you need to look after your own well being. It's your life, and life equals time. Time is the most valuable thing you have. Be careful how you spend it. Once it's spent you can't get it back.
2) She made her bed, she can sleep in it. She's well aware of her situation, but continues doing it. You are helping to enable her continued drug use.
3) You hear about people hitting rock bottom before they change. It's true. Kicking her out might hurt her, but that pain might be just what she needs.
4) You are not responsible for her life. If you do decide to kick her out, remember this. Whatever happens, good or bad, this is on her and the life choices she made. There is nothing to feel guilty about, no matter what you decide and how it turns out.
This coming from someone who was a pretty heavy drug user. I know full well that it didn't just affect myself. It affected everyone around me. I would not have blamed them for cutting me off.