How do I find out if my mother had an life insurance policy?

My mother's name was Katherine Mozingo Melton, dob 12/15/13. My father's name was Arthur Lucas Melton. He died 12/26/1990 and had a life insurance policy which we collected. Mother died 11/11/2009 and I am not sure if she had a policy. All of my father's paperwork is gone so I am no able to look at that to see which company he was insured by. They lived in Hartsville, SC all of their lives and he worked for Sonoco Products Company.