My (16) gf (16) is completely okay with smoking

So I have a really bad history with cigarettes and I really don't respect people that smoke. I have ended 2 shorter relationships in the past due to smoking, the first time i found out the girl was smoking and didn't tell me the second time the girl started smoking one week into the relationship and i broke up with her. My parents have smoked their entire life and i've always hated it and they just never cared. I also hate the smoke from cigarettes as it causes me to cough violently. Anyway I have been together with this girl for over a year and smoking has never been an issue with her as she also didn't like it and didn't want to smoke. I have smoked half a cigarette and it was a really low point in my life. And I told her this and she was completely okay with it and didn't get mad at me at all. And then I asked her if she had ever smoked a cigarette and she said that she hadn't, and even if she had that it wouldn't be a big deal right? and I said that it wouldn't but after thinking about it all night I sent her a huge paragraph in the morning explaining that I really don't want her to smoke that it would really hurt me if she ever started smoking and that i didn't know if i could look at her the same if she were to ever start smoking. Now this paragraph really wasn't good and it was written in 5am and I was just writing down everything that came to mind about that. And after I sent the paragraph she got really really mad at me and told me that she lost almost all respect for me and that now after I sent her that, that if she were to ever start smoking that I would be the last person to find out and that if she wanted to smoke that she would and that my feelings about smoking effect her decision hardly 5%. Now after that we argued for a good 5 days straight and we came to some kind of understanding. She promised me that she won't start smoking now at least, but that this promise lasts until she turns 20 because she doesn't know how she will think then when she's more muture. But that she is allowed to smoke only one cigarette to make it fair because i had also smoked one. I'm happy we came to a conclusion after days of arguing but i still feel like there's something wrong like I love this girl so much and I really just can't imagine her with a cigarette. Like any time an image of her with cigarettes comes to my mind it's like my heart just skips a beat and I hate it so much. I love this girl too much to brake up with her but i really dont know how i would react if she were to ever start smoking. Am I in the wrong please is there any advice you can give me. Also sorry for some grammar mistakes english isnt my first language.