The sitter was the daughter of William Stanhope, 2nd Earl of Harrington (1719-1779) and Lady Caroline Fitzroy. On 17 November 1768 she married Lord Molyneux, who was subsequently created 1st Earl of Sefton in 1771. The present pastel, remarkable for its freshness of colour, was probably executed circa 1768 before the sitter's marriage.
It is tempting to associate the sitter's depiction in military costume with her visit to the Court of King Christian VII of Denmark and his wife Queen Caroline Matilde. Lady Isabella and her sister made a great impression in their pilgrim costumes at the King's masked ball in 1768 and the Queen herself was known to wear military uniform: a painting of her as colonel of the Holstein Guards was painted in 1770.
Lady Isabella's full-length portrait by Gainsborough, now in the National Museums Liverpool, was the artist's first exhibit at the Royal Academy in 1769 and is clearly intended to demonstrate his skill to a London audience.
We are grateful to Neil Jeffares for his help in preparing this catalogue entry.