It all depends on the rules of inpatient rehab at that particular facility. I don't think it's odd or strange at all that she not be allowed to call until her detox is completed.
I guess I'll make the assumption that you and her family are not bosom buddies since they won't tell you anything?
........ but in the meantime, I'd do something for you, let your GF take care of her issues and you should take care of yours, whatever they may be. Al-Anon may be a good place to start so you can understand your role in this.
Take care and keep us posted.