Most Helpful Girl
Is she addicted? Stealing from you to get more drugs? Tricking? If not, leave her be. At least she could admit to you, I would have tried to take that experience to the grave, and I'm open about damn near everything.2
Most Helpful Guy
Well a few things to consider.
1. Make sure she's not using it anymore.
2. Make sure she is not hanging around the people she got it from.
3. Make it 100% clear if she does it again you're through with her.1