On 14 May 1805, she married the 9th Earl of Dalhousie and was styled Countess of Dalhousie.
Lady Dalhousie and her husband had three sons. Their eldest, George, was born 3 August 1806, a captain in the 26th (Cameronian) Regiment of Foot, he died on 25 October 1832. Their second son, Charles, died at nine years old. Their youngest, James, born 22 April 1812, inherited his father's title in 1838 and was created Marquess of Dalhousie in 1849.
When her husband was appointed Lieutenant Governor of Nova Scotia, she travelled with him and their three sons to Canada on the frigate HMS Forth. The family lived in Halifax, Nova Scotia for four years from 1816 to 1820. Whilst there, Lady Dalhousie spent her time in the promotion of science. She toured the countryside with her husband, recommended improvements to farming and collected botanical items. She sent seeds to Dalhousie Castle for the gardens.
In 1820, the family moved to Quebec, when her husband was appointed Governor General of British North America. Lady Dalhousie took on the traditional role of a governor's wife, that of "Patron of literature and the arts".
In 1824, the family returned to Dalhousie Castle and began plans for an extensive garden. Plans for the garden were cut short as the family suffered severe financial losses when their agent went bankrupt. The family moved to a modest farm house in Sorel in 1826 and remained there until Lord Dalhousie was appointed Governor General and Commander-in-Chief of India in 1829.
On the journey to India, the family stopped at Madeira, St. Helena and the Cape of Good Hope. At each place, Lady Dalhousie took time to collect plants and made a detailed catalogue of them. In 1831 she visited the foothills of Simla, along with Penang, near the Malay Peninsula.
He died at Dalhousie Castle in March 1838, aged 67, and was succeeded by his youngest son, James, who was later created Marquess of Dalhousie. Lady Dalhousie died suddenly on 22 January 1839 in the home of Dean Ramsay aged 52.