Whistler's 'Aunt Kate was the sister of his mother Anna McNeill Whistler. She was the daughter of Martha Kingsley and Dr Daniel McNeill. She married Dr George E. Palmer on 23 March 1840 in New York City. They had four children: Julia McNeill (1851-1902); George Erwin (1843-1909); Donald McNeill (b. 1845); and Anna Whistler (b. 1848) (Anna McNeill Whistler's godchild).
She lived in the 'Old Corner House,' on the corner of Main and Wall Streets, Stonington, CT.
Pennell, Elizabeth Robins, and Joseph Pennell, The Life of James McNeill Whistler, 2 vols, London and Philadelphia, 1908 ; Mumford, Elizabeth, Whistler's Mother: the Life of Anna McNeill Whistler, Boston, 1939 ; The Correspondence of James McNeill Whistler, 1855-1903, edited by Margaret F. MacDonald, Patricia de Montfort and Nigel Thorp; including The Correspondence of Anna McNeill Whistler, 1855-1880, edited by Georgia Toutziari. On-line edition, University of Glasgow. http://www.whistler.arts.gla.ac.uk/correspondence.