Link to info on Mary Campbell...Extracts from the info on that site...
Campbell, 'Highland' Mary (1763 — 86) Burns's 'Highland' Mary was born to Archibald Campbell of Daling, a seaman, and Agnes Campbell of Auchamore, by Dunoon, who had married in 1762. She was the eldest of a family of four. She lived with her parents, first, near Dunoon, then at Campbeltown, and finally at Greenock. In her early 'teens, she went to Ayrshire and became a nursemaid in Gavin Hamilton's house in Mauchline.
Burns may have asked Mary to go with him to Jamaica;
Mary Campbell died, possibly from a fever contracted when nursing her brother Robert, possibly as a result of premature childbirth, she was buried in the old West Highland Churchyard at Greenock, in a lair owned by her host and relation Peter Macpherson.