Emily Whistler may have been a remote relative of JW's.
In the 1881 census she was listed as unmarried; she was then the Principal of Hilldrop House School, Lewisham. She was then living with her widowed mother Rosella (aged 71) and sister Julia (aged 30). In the 1901 census she is listed as living in Kensington, London.
UK census 1881, from http://www.familysearch.org (accessed 2004); UK census 1901.