CameraJen...
Welcome to the Board. When I read stories like this -- 17 year olds getting into heroin -- it makes my heart sink, and I know I'm not the only one. So I'm really sorry for what has brought you here, but grateful you are here.
The pattern that your AD is following -- pick up, detox, pick up again, detox again -- isn't anything new. And while I don't know your AD and I'm not inside her head, I suspect she's not ready to do the hard, necessary work to recover.
May I gently suggest that your husband's not doing her or himself any favors by "watching her like a hawk until she detoxes". All that is doing is strengthening a codependent dynamic which neither you, your husband, or you AD can afford.
As for what to do, I can't tell you that. On the one hand, coming off opiates should be done in a safe, clinical environment. On the other hand, chances are pretty good she's going to pick up again, and based on that, you shouldn't pay for it.
So, I'll defer to our "moms". We've got a lot of them here in various stages of healing and recovery. Keep an open mind and pay close attention to what they share with you. It could save your sanity.
Again, Welcome to the Board, and you, your husband, and your AD will be in my thoughts are prayers this evening.