Slink Trev's mate Claire says:
I have gone through the same thing with friends and boyfriends in the past. Everyone knows the facts with smoking, so it baffles me that people still start. You are an ace mate to try and get her to see sense.
Are you sure she knows all the health issues associated with smoking? For example, increasing her risk of cancer, heart and lung disease, as well as giving her bad skin and yellow teeth? Not to mention the cost of funding the habit.
The thing is, preaching to her about all this probably won't stop her wanting to be cool. Though as both you and I know, it obviously isn't cool, and is not the key to being popular amongst your school mates.
Talk to her, and ask her to imagine how her parents might react if they found out she was expelled for smoking - it might put her off.
If you can't reason with her that way, you need to show her that it isn't cool. If you know anyone popular at school who doesn't smoke (especially someone she fancies) point them out to her. She'll get more respect from people for not following the crowd anyway.
If you can't get through to her, and it doesn't feel right talking to a teacher or her parents about it, know that you've tried. She's going to grow up and realize how silly she is being eventually. But with a mate like you by her side, I'm sure she'll find the right way.
Check out some info about smoking on The Surgery advice pages.
Don't give up on her!
Cx