I don't have a subscription to Ancestry, so I can't look at the document. Who was the informant? "...on the death cert she names her dad as George Ringstaff Stewart and mother Fannie..." Stella didn't give the information on her DC, so accuracy only as good as the knowledge of the informant.
I tried SSDI, no Stella Lewis with death date of July 1971. So I tried just using last name of Lewis, death July 1971 and last residence SC. None named Stella or Edna.
Do you know her Soc Sec number?You can obtain a copy of the application she filled out and that should have names of her parents, her residence at that time etc.