The sitter was the younger daughter and coheiress of Richard Powis of Hintelsham Hall, Suffolk, and his wife, Lady Mary Brudenell. On 22 August 1761 Lady Kildare wrote to her husband 'Mr. Stopford is going to be marry'd to a relation of mine ... a pretty agreable girl, Miss Powis, daughter to Lady Mary Bowlby [formerly Brudenell, daughter of George, 3rd Earl of Cardigan, remarried], she has a £20,000 fortune' (B. Fitzgerald, Correspondence of Emily, Duchess of Leinster, 3 Vols, Dublin, 1949-53, I, p.106). She married James Stopford, afterwards 2nd Earl of Courtown (1731-1810), on 19 April 1762. The sitter's elder sister Elizabeth Powis (1736-1826) was also painted by Reynolds (Mannings, op.cit., pp. 379-80, no. 1465). Reynolds's sitters' books appear to indicate that the sitter was most likely painted in 1762.