First and foremost, sit down with your wife and if she is open to it...watch
The Union: The Business Behind Getting High

I too found my daughter as well at about the same age. And feel as you do. It's really all about open, honest communication...rather than autocratic, authoritarian dictatorship. It's worked wonders for me to just be a fellow human being who genuinely cares and can offer articulate perspectives to navigating this thing called "life".

To me, it sounds as if your wife is afraid for her on some level. Maybe there was an negative experience with the plant, or something else. I believe it's closer to "protection from harm" than anything else. But I would argue that force-sending someone to a rehab for cannabis out of fear would be more harmful than not. Fact is...not one human being on the planet EVER has died from smoking the plant. It has a thousand uses, all good. If you want to dive into researching the subject...start with the above video first.

Then check out one of my channel's videos here:

That will get you started....and just surf around the channel for more insightful videos both created by me and shared by others. Hope this helps. Feel free to visit my channel here - https://www.youtube.com/user/ScholarConsciousness/videos

Take care...Peace!