My daughter banged her front tooth really hard falling off of a picnic bench. It too was loose. It went from white to gray but never caused her any problems so we (her Pedi and I) decided to just keep an eye on it. That was 3 years a go. It is now loose just like the one next to it.
Putting my Pedi RN hat on, I do know that the biggest risk is that the tooth will develop an abcess. The symptoms of that would be pain and a tell tale pimple like blister on the gum directly over the injured tooth. If that happens she really needs to see a dentist.
If I can answer anything else please feel free to e-mail me!