Katherine Duff was the daughter and heir of Adam Duff of Drummuir. However, when she inherited the estate it was burdened with debt. The Duff family encouraged her marriage to Alexander Duff, who paid off the debts. Alexander Duff served as M.P. for Inverness. The couple had a large family. Alexander Duff died in 1726. Their eldest son, Robert, was weak-minded, and Katherine Duff managed the estate on her son's behalf.
Lady Drummuir was noted for her charity and carried a purse full of coppers to give to the poor.
In 1746, Lady Drummuir's house was said to be the only house in Inverness which did not have a bed in the parlour, and was the house in which Prince Charles stayed prior to the battle of Culloden. After the battle, Cumberland billeted himself in the house.
Lady Drummuir died in 1758.