Maud Mary Monk (1862-1942), née Waller, was the second daughter of Major Charles Bullen Waller and Emma Piggott. She had twelve siblings. Her elder sister Edith Emma became Mrs Marzetti. On 8 November 1887 Maud married Richard Powis Monk. They had five children. Her uncle Pickford Robert Waller was an English designer and collector.
According to Pickford Waller, Scherzo in Blue: The Blue Girl (YMSM 226) was painted from Maud, whom he described as a beautiful child and a pet of Whistler's. Waller recalled that when the portrait was halfway through it was put aside, but that it was sent to the Grosvenor Gallery for the private view and taken away directly after. Maud also posed for Study of Maud Waller for 'Scherzo in Blue: The Blue Girl' (M.846).
UK census 1881, from http://www.familysearch.org (accessed 2004); Young, Andrew McLaren, Margaret F. MacDonald, Robin Spencer and Hamish Miles, The Paintings of James McNeill Whistler, New Haven and London, 1980; MacDonald, Margaret F., James McNeill Whistler. Drawings, Pastels and Watercolours. A Catalogue Raisonné, New Haven and London, 1995.