Mary A. Bosanquet was the wife of Henry Anstey Bosanquet (1828-1861), a barrister. They had three daughters, Mary, Edith and Carrie.
She may have known JW in the mid-seventies, since her name appears in an address book (#12714). The family was prosperous (in 1881 they had seven servants).
UK census 1881, from http://www.familysearch.org (accessed 2004); Foster, Joseph, Men at the bar, London, 1885, p. 45.