Parenting Teenagers: Marijuana
The "It's my body" defense can be a showstopper, and ultimately the decision will be your teen's to make. But try this:
The reality is that when it comes to smoking, drinking and doing drugs, it's not just about you. It has an impact on everyone around you, whether you know it or not. You start smoking pot thinking that it's nobody business as long as you don't hurt anyone. But because of your example, one of your friends starts smoking pot, too. Or your brother or sister. And maybe they don't handle it as well as you, and get in trouble with the law or their health. Girlfriends, parents, friends, schoolmates, even innocent bystanders can all be affected by your actions, now and in the future and far beyond your control.
It's possible that reminding her that she is connected to all those people and others she can only guess at may make her feel a little less alone and a little less inclined to get involved with drugs in the first place.