Ex Wife Might Have Stolen Sons Inheritance

My ex mother in law unfortunately passed away. She left my son 15k specifically to get a car when he turned 16. The Ex wife bought a car for my son with the money, and not long after, my son totaled the car. (Everyone's ok) Insurance paid out 8k and they got another 2k back from the service contract so 10k total. My son was paying the insurance on that car with his own money earned at his job.

She uses the 10k to put a down payment on a new car for her, and told my son he could have her old car, which is worth about 8k. She's now refusing to let him drive her old car, and has even threatened to sell it. The Ex wife says he spent his money on a car and totaled it so his money is gone.

I don't agree with that statement and feel at the least he should either have the insurance settlement/ service contract refund to buy a different car, or she sold him her old car when she used that money for her new car?
Thanks in advance to any and all comments