My response:
The State of Virginia is a "separate property" State. In a separate property State, each spouse holds all property he or she acquires -- before and during marriage -- in his / her own name, and has the right to access, control, and dispose of only his / her own assets.
As such, your father's Estate is the only "entity" responsible for his bills - - not your mother, directly. Of course, any money that the Estate is responsible for paying out is going to affect Mom, i.e., there will be less money going into her pocket as a result of the Estate having paid the leftover bills. But, no one can come after Mom "directly", as they would be able to in a "Community Property" State, such as would be the case in California, and other Community Property States.
Mom needs to open a Probate action with the court, and all creditors need to be notified of Dad's death. That way, the creditors can make their claims on the Estate, and the court can issue the proper orders regarding the debts. If Mom doesn't do this on her own, any of the creditor can "force" a Probate of the Estate to be opened.
If Dad's Estate has no money in it, the creditors will eventually "write off" the debts as being uncollectible.
Good luck to you.
IAAL