Stop Smoking Forum - want girlfriend to stop smoking

My girlfriend is 27 years-old. (I am 29.) She has never smoked (cigarettes) in her life, but her mother has always smoked. I was a casual/on & off/social smoker when I met her just over a year ago, but took our relationship as a good excuse to quit. I told her that and stopped smoking all together, aside from once when I came over on a stressed-out night and told her I'd smoked a cigarette with a friend. She said I stunk and made a disgusted face.
About 6 months later, she confessed to me that she'd been smoking for the past 2 weeks. I tried to be cool about it, but felt really wierd about her doing it behind my back. I told her and began to smoke with her. For whatever reason, it bothered me less if I smoked, too (even though I knew it wasn't the "right" thing to do). We both smoked for 1-2 months and finally I told her I wanted her to stop smoking and go to therapy before we moved in together. She initially acted as though she was excited (she's wanted to move-in together for a long time and I've been ambivalent). However, she later cried to me and told her how crappy it felt to "not be accepted as (she) is" and to "have conditions put on her". So, I backed-off, but we both quit smoking together. She said she would go to therapy, but "in her time".
About 4 months has passed since then and I came to realize (through smelling her breath) that she was smoking again. I was pissed about the lack of communication (again), in particular and was vocal about it. I told her I wanted her to quit. She said no and suggested it wasn't an issue. She was "just having 1 every once in a while". She says, "why can't I just smoke for a while? I don't understand why it has to be such a big deal." Somehow, it totally bothers me (smelling it on her breath; seeing her volunteer herself for a major addiction; making this part of her life, which I didn't sign-up for). She also shared with me that she never wanted to smoke in her life until the night I came home early in our relationship smelling like cigarettes. She said she felt "shut-out" and I find myself feeling that way with her smoking, too.
I've told her this round that I don't want to start smoking around her. She didn't buy any until I did one night after we had a fight (it was like I was getting back at her in an immature way! I was tired of being the strong one!). She bought a pack the following night and has started smoking every day since. Now, she's smoking daily and says it's related to her job stress. I'm working really hard to not start again, too, but I find that it eases my frustration when I do it with her. (At least I don't smell it on her so much when I do!)
So, we're still talking about moving-in together. I don't want her smoking to become a power struggle, because I know I'll loose. I'm wondering if it's appropriate of me to say something like, "So, I realize that with your smoking, things are really tough and stressful at work. I'm thinking that it's not the best timing for us to move in together." What do people think of that? The second part (and what I'd really like to say) is, "I'm having too much of a hard-time watching you take-on a major, health-harming habit without doing the work to look at yourself, learn about your triggers, and find another way to deal with them. I can't control what you do, but I can control how I relate to what you're doing and I'm not comfortable with us moving-in together with this going on." What do people think!??? Thanks for your help!