Did a search on line and came up with the same census records as you. I did come across a marriage for a LIZZIE STEWART who married 2-27-1903 in Carter Co which names her parents as ST. CLAIR STEWART and MARY WALLACE.
I found MARY STEWART living in the 1930 census of Carter Co Ky at the age of 88 and subsequently a check of deaths in Carter County showed a MARY CARTER who died 10-2-1930 at the age of 84.
I came across the entry for her death for 1930 and it identifies her parents as GEORGE WALLACE and NANCY FISHER
The DC for MARY is #26652 and until I can view it on microfilm cannot ascertain if her husband is mentioned or the place of burial. You could contact the Boyd Co KY Library at their website and see if they could look the DC up which they have the KY DC's on microfilm.
I realize the dates do not actually match up but so it is in many genealogy records.