@Seff:
It actually is nice that you care enough to want her to stop, but in my experience, trying to change people very rarely gets them to change. They have to want to change in the first place.
I had a similar problem with my girl. I honestly didn't know how to deal with her smoking, so I pretty much just let her be and never gave my opinion about it. Not once did I judge her, or told her to stop. She knew that I wasn't into smoking, so initially she would try to hide this perceived flaw by going out to buy some cigs without my knowledge. When I eventually found out, I told her it was okay.
Funnily enough not doing anything on my part eventually resulted in her giving up smoking completely. I'm not sure what happened, she just decided to quit one day and told me, "Thanks for not judging me when I was smoking. I realize now that I don't really need them anymore".
Of course, different people have different reasons for wanting to smoke. It's a lot better if you try to understand that underlying reason, and realize that not everyone has impeccable self-control or are capable of coping with life without smoking. Just be there for her, and give her some space to think whether or not smoking is good for her. I don't think pressuring her to stop, especially with ultimatums like "if you don't stop, we can't work out", is the best way to go about it. Making them feel miserable about their problems just doesn't do wonders for someone.
But who knows? Maybe your methods might work as well. I'm not confident enough to say that my one experience fits everyone else. Just some food for thought though.