She might only be 17 and she's still your baby and all that crap but talk to her like an adult. Weed is probably gonna be smoked. Tell her you wished she wouldn't and you won't accept it but you understand it could happen eventually. Tell her about the first time you smoked, the last time you smoked, why you don't smoke. She's more likely to open up to you about it. More importantly, IMO, pound into her head the dangers of every other drug, especially prescription drugs. Prescription drugs are extremely dangerous and so few people understand that, especially high schoolers.