Her husband, John, should have been heir to the dukedom, which was only able to descend through the male line; but he was ineligible since his father had fought in the Jacobite rising of 1745 and consequently been attainted in the blood.
Charlotte, however, had succeeded to her father's title of Baron Strange (which could descend through the female line) and consequently held a higher position in society than her husband.
Thus, just less than a month later on 7 February 1764, the House of Lords deemed John as the rightful heir to his uncle's title (notwithstanding the attainder of his father) and he succeeded him as 3rd Duke of Atholl, whereupon Charlotte became Duchess of Atholl.
She inherited the sovereignty of the Isle of Man from her father on his death but sold it to the British Crown in 1765 for £70,000 and an annuity of £2,000 per year.
The duchess died on her 74th birthday in 1805 at Barochey House, near Glasgow, and was buried at Dunkeld.