Angelina
Very good it went so well,I doubt a lot they would accept it.
It seems the main fact was she is very happy with you and the fact she only have to wear it during your dates.
I understand it was a hard and intense talk,but the outcome was good,so it was worth it.
Her parents haven't asked for a copy of the keys,in case of need?
Is she "happy" to get her own belt soon?Anyway,it should be your grand mother who does it(maybe with your help),not your father.Or her parents,but I doubt they would accept.Or he could use the measure of your precedent belt(the one she wears presently).