Advice Please!

My friend just started drinking at school, we both smoke weed recreationally and I think that’s ok but I don’t know how to handle her drinking and smoking at school. She has a history of self harm and I feel like this is another way she’s hurting herself. I would tell the guidance counsular at school but she’s not very useful and has only caused trouble when it cones to these things. Please give me any ideas or advice, thank you!!