I think her car was in fact her fathers, and presumably in his name as well. A few threads back we got into the details of who owned what, and I'm not certain, but I think I remember the car being her dads, and she had just gotten it back, recently.
Good question. I wonder if lighter and bottle of accelerant was found at the scene. Your theory is plausible but she still would have had another car there to get her home. And a friend would have came forward with the accidental reason by now. Jmo