How can i get my girlfriend to quit smoking?

My girlfriend smokes. I want her to quit. She doesn’t do it around me but I can always smell it and I just hate how it can effect her health. I have tried to use guilt, saying how its unhealthy to everyone but she just gets pissed when anyone tries to lecture her. she knows how bad it is and she kind of wants to quit. besides her smoking she is the most amazing girl ever.