NTA. I am a 20yo and almost never had any problems with my parents or drugs. And also my view on this might not agree with others but I still hope it helps you!

Your daughter sounded very impressive: good grades, good behavior, ...

As a parent, it is in the best interest to do the right thing for their kid. And in my opinion, sending her back to boarding school is the right thing.

She supposedly hung out with kids that took drugs, doing bad stuff and having problems with the cops. That is not what a parent likes to see. Seems like a path, sending her into a dark future.

If she is not going to the therapy sessions, ..., whilst doing nothing to get her on a good path again, the only option is the thing you did.

You only have to hope, that she'll appreciate this in the future if she gets better again. Because this plan can also take a bad turn of events. I've seen a lot of stories on here, where this was a deal breaker in the relationship. Please be careful and think this one through. You'll know what's best for your daughter!

I hope this has helped you and stay healthy and safe.