I fully understand your predicament. Since finding in my daughter’s purse small sachets of a white piwder, which turns out to be a mixture of ketamine and cocaine, I’ve been reluctant to go head-to-head with her on it as it would destroy any trust we hold between each other. The conundrum being that I can’t believe a word she says anymore since she started substance abusing. I’ve since been given the advice to firstly stop her financial source, she’s only 17 and still a school girl, and then ‘pick my fights ‘. It feels like a hard road ahead of being very firm and not loving. As was said “Don’t use the word love in any discussion!”
Wish I could help more.