While I agree that this is very sad, I also have some questions that never seem to get addressed in the news articles.
The man who was killed, Justin Walker, was an adult. Didn't he have auto insurance because I'm pretty sure the insurance company is the one that pays for the accident clean-up and towing (although not the storage in case of a criminal trial). And if the vehicle was stored as evidence in a criminal trial, why didn't the city store the vehicle, not the mom? It seems to me if the mom is storing the vehicle, then the chain of custody of any evidence that might exist has been voided. In short, if the mom is storing the car and has access to it, then any evidence she might say exists is immediately nullified.
Now I can see the mom getting the bills and having to pay them if she is the executor of her son's estate. However, if her son died without any assets - or assets that got eaten up with paying off his bills - then there is no money in the estate to pay these bills. SHE doesn't have to pay any debts owed by her late son. She does have to pay the debts owed by her late son out of his estate - his remaining assets. She isn't personally liable for his bills, though. So if she isn't working and living off of his remaining assets, it is painful to think that she'll have less to live on because she has to pay off his bills. But that is how inheritance goes. You can take the money then leave the decease's creditors hanging.
Plus it was implied in one article that she did receive some victim assistance funds that helped with her counseling and funeral expenses.