If the assets were liquidated after her death and then deposited in the POD account, those assets weren't handled properly (unless they were also POD). At this point, it is best to consult with an attorney as to the best way to unwind the deposit of cash after death, if that's what happened.
The son was entitled to the assets that were in the account on the date of death. Other assets, unless they were titled the same, were subject to the terms of the will and the proceeds of their sale should have been deposited in an estate account, not the POD account, for distribution per the will. (Again, assuming those assets were not also held in a POD account.)
