I've been through a similar addiction, with smoking though. I smoked from when I was 15 to about 21. My girlfriend at the time wanted to quit as well. At any rate, we both quit (it's been about 12 years for me) and I went to her palce one day (about 9 months after quitting) and sure enough, she was puffing away.
I know it's hard to support someone when you are clean, especially because it's easy to say "well if I can do it, anyone can". If you truely love her, then help her through it, so long as she wants to quit. Some people don't. It took my father being hospitalized in the ICU for a week with tubes in his lungs for him to quit smoking after 30+ years. If she wants to get better, she accept the help that you offer. This doesn't mean you have to be a softy with her, but also remember every person is different. Try to help her through the things she finds the most difficult about quiting. You may want to give her some pointers on how you handled it when you were going through it.
We're all here for you man, drop any of us a PM, or a line whenever you want to talk.