I agree that this photo doesn't help your cause at all.
As I look at the "damage line" across the grill and the LACK of damage to the bumper (this is a crumple bumber-energy absorbing) it looks to me as though someone rear-ended a trailer (as in tractor-trailer rig). The damage line appears to be at the correct height for the rear trailer guard. Also, I notice that the driver's side headlamp assembly is gone but the connector and cable are there. Further, there is no evidence of DEBRIS anywhere in the photo. Such a "hit and run" while parked should have debris all over the place. I also note that no mention of any transfered paint is mentioned in the report. Seems to me that there should be some paint on this wreck if it was indeed hit by another car (which I don't believe. A trailer yes, car no.) I would expect such a crash to make a LOT of NOISE and seeing as it's a residential area, someone should have HEARD something and possibly looked out their window. I know that if such a "hit and run" occured in front of my home, I would have summoned the police immediately in part to help the owner of the vehicle and to remove the wreck and debris from the road (we have children who pay around here.)
It looks to me as;
1. The vehicle WAS NOT damaged where it is parked in the photo. The car has been MOVED since the accident.
2. The damage shown is consistent with impacting a barrier that is high off the ground (higher than the bumper.) Perhaps a trailer guard, highway guard rail, etc.
3. It is unlikely (IMO) that this was caused by another vehicle BACKING into this car because of the velocity needed to cause such damage.
It is plausible that the vehicle was in a moving accident with another vehicle or stationary barrier. I have to wonder why you don't post a photo of the damage on the driver's side of the vehicle.
I suspect, as the insurance company does, that it is possible the vehicle was in an accident (likely driven off the road or into a barrier) and was then driven/towed to the location where it was photographed. It is also likely that the owner didn't have insurance at the time of the accident, so the owner purchased insurance, waited a few days and made a claim of "hit and run." This type of scam goes on all the time.
I'm not accusing the author but this is HIGHLY SUSPICIOUS and I don't blame the insurance company for taking some time to thoroughly investigate the matter before paying out.
It would appear LESS suspicious if there had NOT BEEN A LAPSE in insurance. If what the author wrote is truthful, I think the author should get her SON to pay for the damages because, quite frankly, something doesn't smell right.
I almost forgot. Another possibility is that this car was DRIVEN into a parked vehicle and somewhere out there in CA someone is honestly trying to find out WHO HIT THEIR PARKED VEHICLE. I have to wonder if there are any other claims of "hit and run" of a parked vehicle (trailer) anywhere in CA.
Sorry, but I'm not buying this fish tale and I don't think the insurance company is either. If you son truly had your car I think you should tell him to get a second job and start making payments.