Christie's overview notes for her 1831 portrait are informative: "The only child of Henry Vane-Tempest, Bt. (and Anne, Countess of Antrim - gogm), Frances Anne was, at the death of her father in 1813, one of the richest heiresses in the country. Her beauty was occasionally remarked upon but references to her temperament and hauteur were more prevalent, as she matured into a woman. In 1818 she met Charles William Stewart, heir presumptive to his half-brother Robert, and later 3rd Marquess of Londonderry, who was twenty-two years her senior. They were married in 1819; it was an ideal match. Frances Anne’s pride met its equal in her ultra-conservative husband, and he revelled in the vast wealth and territorial power which the match brought him, including her ancestral home, Wynyard Park, County Durham. The couple’s income was huge, and was enhanced by the dramatic expansion of their industrial interests. They were dedicated patrons of the artist Sir Thomas Lawrence who painted the double portrait of the Marchioness with her son, Viscount Seaham circa 1828 (detail above) and whose earlier half-length portrait of her had so captivated Tsar Alexander I, Emperor of Russia. After her husband’s death in 1854, far from handing control of the huge coalmining and coal-shipping concern that was the basis of her fortune over to her son or agents, and retiring into obscurity, she established herself at Seaham Hall as the active and effective head of the business and, furthermore, was active in the electoral politics of the county and city of Durham."
Christie's lot notes continue, "The portrait may have been commissioned to commemorate the coronation of William IV, which took place on 8 September 1831. Frances Anne must have made a spectacular entrance to Westminster Abbey, for she was mentioned in The Spectator as ‘The next lady who created a buzz of admiration, was the Marchioness of Londonderry; to form whose attractions, were conjoined the beauty of the first [Marchioness of Hastings] and the jewels of the second competitor [Duchess of St. Alban] for public honours’ (The Spectator, 10 September 1831, p. 871). The remarkable jewels on the front of her robes include a number of pink topazes, one of which was given to her by Tsar Alexander I in 1821, who had been greatly taken with her on their first meeting in November 1820. Frances Anne also sat for a half-length portrait and a full-length with her son (...) by Sir Thomas Lawrence (K. Garlick, Sir Thomas Lawrence, Oxford, 1989, p. 229, no. 510a and b)."
Her Wikipedia article mentions she promoted the political career of Benjamin Disraeli, today mirrored in the manner of American hereditary aristocrats funneling money to support politicians who support their economic interests. It also states, "...Through her daughter, Lady Frances Vane, wife of John Churchill, 7th Duke of Marlborough, she was the great-grandmother of Sir Winston Churchill..."