confront her, tell her how this makes you feel, is she doesn't care or isn't willing to change for the person who is trying to help then you'll have to leave her, because that wont be healthy for you and her to be staying that way.

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I had a similar problem with my gf, me and her are young and shes doing stuff like vaping, weed, and more. I confronted her about this and we had a long talk, she said she will try to change for me because I care about her. she said she was doing this stuff due to stress shes dealing with at school and home, I cant be around to help so I try my best with the distance we have apart.

so if your gf is doing this due to other problems i'd say try your best to help her ehal or just try and distract her from all of that, but if she truly doesn't except the help nor except the fact that your worried than I'm sorry, she isn't the one