When I go to https://jeffersondavis.rice.edu/Genealogy.aspx
It shows descendants in the “Mary Ellen Davis” family continuing into the early 20th century and having 6 children here and some over there. Some of the other family branches do as well. I’m not a genealogist but it seems possible that she could be a child of someone descending and born in the not too early twentieth. The charts didn’t entirely make sense to me so I could be reading wrong.
and even if so, how would that make her a descendant of Jefferson Davis?