It would depend on when he served and as long as they were not divorced prior to his death. I would get in touch with a Veteran Service Officer in your area to go over any potential benefits available to your mother. You can find a VSO near you through the VA's website at OGC - Accreditation Search
Click on VSO Representative, Enter in the City and State and it will populate a list of people for you that you can contact. VSOs provide assistance free of charge to veterans and their dependents. Should you have any more questions please let me know.