Harriet Hartley?
I can't find anything online regarding this "mystery woman." Does anyone have any details on her, her connection with the Le Prince/Whitley families, or anything?
She's not in the 1871 Roundhay Census, but "Mary J. Hartley" is. She would about 19 by 1888. Interestingly, Louis Le Prince (as "Augustin") is living with the Whitley's at "Roundhay Cottage" with his wife and newborn daughter in 1871. Given that a servant (Phoebe M. Eadson) lives with them in that time period, it's possible that Ms. Hartley was another servant of the Whitley's 17 years later.
Information can be found here ( http://homepage.ntlworld.com/nev.hurworth/1871CensusRhay.htm ).