If she doesn't have a charger, the phone battery could be dead. Any friends of hers you could check with? You could tell them that your first concern is her safety, and that if you don't talk to her you are going to have to call the police. That might be enough to at least get her to call so you know she is safe.
Otherwise, if she has never done anything like this before, I WOULD call the police. If they won't take a missing persons report (policies vary among departments), then report the car stolen. Once she is found, THEN you can worry about what to do going forward.