I know this is a long shot, but maybe worth exploring. Some of my ancestors are the 17th Century Moores (Gov. James Moore of Charles Towne was first.), who traveled all over South Carolina. Two of the Moore boys, James and John became Indian traders, and one of them married a Cherokee named Mary. I have their male line of descendents but no females. By 1770, when your Mary was born, Abbeville County had not yet been formed; it would have been 96 District, but it is still in the territory that could have been populated by the descendents of my James, John, and Mary Moore. See? I told you it was a long shot. But I'm big on the reoccurence of given names in a family.