Ok, I definitely agree about the need for intervention, and sooner not later. I could tell all the same stories about my brother (drugs, alcohol), friend (eating disorder), other friend (drugs)......etc. I am constantly an advocate of getting in people’s business because it is better for them in the long run, not to regret not having helped when one could, etc etc etc.
BUT! I really really disagree about the method of sneaking onto her computer or email. I’m not a parent, but I was a teenager whose parents trespassed those limits of privacy. It DESTROYED our relationships and more than a decade later (with almost no contact) there’s absolutely no sign of it ever resolving. At 17.5, you are nearly an adult. I understand the legal stuff about minors, but this is a question of relationships. She is an individual, with rights, an identity, a life,... (all those same things we all have)... and she deserves RESPECT. I felt, and still do, that my parents couldn’t separate that identity—- I was part of them or however you’d phrase it—and couldn’t make that transition into perceiving me as an equal and separate individual. It can be something as simple as not opening another person’s mail (then) – today, I guess the parallel would be snooping in email (although that strikes me as one notch further). At 14–15-16–17-18–19 (very much depending on the person/culture/circumstances) you are TRANSITIONING from child/youth to adult. It obviously can’t happen overnight on the 18th birthday, so you have to consider it a gradual process—and your doing so will create the possibility of a successful transition. (That might seem like a tangent, but I think that underlying thinking is very relevant for how you handle this situation.)
A serious heart-to-heart, a group discussion with family or friends, a letter (less recommended), a spontaneous just-the-two-of-you vacation somewhere fun (if it’s long enough, an addiction would surface then), telling a story of your friend who ODed, simply explaining your position (talking like an adult! woohoo!), whatever you think is best in the circumstances…. is better than something you clearly understand to be wrong. You can’t teach right and wrong by doing the ‘wrong’ thing, and you can’t teach how to have healthy interactions and relationships if you don’t do them. Helping her is absolutely the right move for a loving parent (or any loving person who knows her), but you have to do it in an adult (mature/respectful/honest) way. Imagine having a good conversation with her after breaking into her laptop – hard to imagine, right? Why add a ‘wrong’ on your side when you don’t have to? Increase the likelihood of a successful outcome in this particular situation, and the larger situation of her transition to adulthood (with all the choices and responsibilities that come with it), by doing the right thing every step of the way. It may be harder for you now (having to creatively come up with an alternative to the “easy way”), but it will pay off in your relationship with her, and in that way could have just as significant implications as the drugs themselves.