Emily Sargent did eventually turn up in the 1901 UK Census. A kind person at British Genealogy Forums winkled her out.
Emily Sargent, born Liskeard, 1871, who is a nurse/servant for Cuthbert Knocker and family.
RG13/2190/13/18 (Copyright TNA)
Lieutenant Colonel Cuthbert Knocker, if you please! And born in India, to boot.
We still cannot discover how and when Gwendoline got away from New Zealand.