Please help. Niece trying drugs

B

My sister (only sister) has 3 kids. I love the kids, I helped babysit etc. The oldest is 11 and I just got told she’s tried weed twice at school. I want to talk to her and explain how dangerous it can be because things can be laced with something. How can I talk to her? I’m 24 and mature and she adores me. But what do I say for her to understand it’s not right.