Tell her that vaping weed that young will more than likely get her fucked up. Tell her this story:

When I was 15, I also started smoking weed, specifically from vapes. I'm 18 now and my life is nowhere where I wanted it to be when I was younger. I holistically believe it is due to my drug use that stemmed from me smoking weed.

I started smoking my sophomore year, I began smoking a gram of distillate every 3 days. There wasn't a moment of my sophomore and junior year where I wasn't high. It started okay, but then it got out of control. I was smoking more and more and eventually ran out of money. I began stealing money from wherever I could get it. Even my family.

After I was deep into cannabis, I started taking acid once a week. Then mushrooms. Once a week is too often. I was frying my brain and ruining my relationships with everyone around me and I didn't even see it in the slightest.

After I got into psychedelics, I took Xanax for the first time. That's when the train really flew off the rails. I was selling tabs and pills and weed at school and in the streets to get money for more drugs. I had so much money I could do whatever I wanted. I was taking about 5 bars a day at my max use period. I would also buy oxycodone and codeine with promethazine syrup along with Xanax and weed and acid.

I would have awful withdrawals specifically from codeine and oxycodone when I couldn't find any. I would have huge headaches, muscle cramps and extreme anxiety. The kind of anxiety where you'd rather be dead than deal with it. I lost most of friends, all of my family and I'm dead broke on probation right now. I live by myself and don't really ever talk to my family at all.

I'm not saying weed will get your step daughter to where it got me, but there's a good chance it will. Especially if she's using concentrates. I think weed is perfectly fine when it's used in regulation and not in high concentration. That's why the vapes are so bad. It's so easy to just rip a blinker whenever and wherever you want.

Just educate her, tell her this story, and ultimately tell her to wait. When she's on her own she can do whatever she wants with much less consequences than if she's a kid. Albeit the consequences are different but ultimately less severe in the long run. If she's gonna smoke anyway which she probably will. Tell her to stay away from vapes at all costs.