Q: My AWD Vibe was towed &rear differential is damaged.Can I prove it was caused by tow? Was quoted $1400 teardown to determine cause

My 2004 AWD Pontiac Vibe was towed by my insurance company because it wouldn't start. It turned out to be the starter needed to be replaced. When towed, I stated it was an AWD and it was not towed on a flat bed, but towed with the front wheels up, I am not sure if dollies were used on the rear wheels. After the tow, there was damage to the rear differential, it started making a whirling noise especially if I was going faster. This was confirmed by a local Chevy Dealer. My insurance company stated they need proof of whether the damage is wear and tear or from the tow by having a "teardown" for my car. The dealer quoted between $1400-$1800 just for the teardown. First, can it be determined that the damage was caused by tow vs wear and tear? Second, is there anything else that can be done to prove how the damage was caused that won't require as much man hours?

My car has 169360 miles.
My car has an automatic transmission.