Maud Glen Coats, Duchess of Wellington (d. 1946).

Note:

References:    

Ormond, Richard and Elaine Kilmurray, "John Singer Sargent: complete paintings; volume 3, The later portraits," New Haven, CT: Yale University Press, 2003, no. 514.

McKibbin, David, "Sargent's Boston," Boston, Museum of Fine Arts, 1956.

Illustration:    

Ormond, Richard and Elaine Kilmurray, "John Singer Sargent: complete paintings; volume 3, The later portraits," New Haven, CT: Yale University Press, 2003, pg. 170.