She was the daughter of Emma Maria and James Burkitt. Her mother, Emma Maria Cranwell, daughter of the bootmaker Joseph Cranwell, had married James Burkitt, a gold beater, on 19 August 1868. After his death, the widowed Mrs Burkitt was Whistler's landlady from 1898-1901, until, on 11 July 1901 she married Louis Edward Blackwell, who was described in the marriage certificate as an 'Art expert'. Sophie was born on 14 December 1882 and married W. E. Griffiths on 24 August 1918.
Sophie posed for Rose and Gold: The Little Lady Sophie of Soho y504 after her younger sister fell ill; eventually her sister Edith posed for The Little Lady Edith of Eden y541. Edith, explaining the title, said that Whistler 'told my mother my sister was 'fit to be a princess.' She recalled that the painting was finished at 110 rue du Bac in Paris.
Shaw, Edith and Margaret F. MacInnes, 'Four Years with Whistler', Apollo, vol. 87, March 1968, pp. 198-201. Young, Andrew McLaren, Margaret F. MacDonald, Robin Spencer, and Hamish Miles, The Paintings of James McNeill Whistler, New Haven and London, 1980 .
UK census, 1891, 1901. 'Edith Burkitt' and 'Emma Maria Cranwell', Ancestry.com.