Hey Steph. Welcome to the forum! All of this happened over a magazine? I guess I am confused a bit as to why someone has a magazine delivered to a clinic, but it must be because they sit in the waiting room quite a bit.
I am not lawyer so whatever I tell you would just be my best guess / opinion which in the end is not going to help you that much. Your best best would be to talk to a lawyer. I am sure clinics have a lot of leeway as to who they accept and rules for discharge and since they were offering to detox her it is most likely going to be an expensive and uphill battle for you. I doubt you can sue someone saying they made her relapse, but again this is just the opinion of an ex-junky.
Sorry you are going through this. I hope it gets resolved to your satisfaction. Take Care!