Mary McColl's parents were Alexander McColl and Mary Campbell. Alexander was born about 1780 in Marlboro Co., NC, to Duncan McColl, an immigrant from Appin district, Argylshire, Scotland. Duncan was born about 1754 and died about 1825 in Marlboro Co., SC. His wife was Mary, last name unknown. She likewise was born in Appin, in about 1754 and died in May, 1828, in Marlboro County.
You can find Duncan McColl on sheet SC-3 of the Clan Cholla Genalogies. I have verified everyone on the entire sheet.