Wow - I never expected to wake up to so many (or any) replies! Thank you, everyone, for reading and responding.
I can't tell you how exciting this is - it has been a family mystery for years.
And if I can help at all with research at this end, please do let me know.
So, in answer to the questions:
Leanne: Yes, Elsie's married name was first Chandler, then Blore.
Merlin, I don't know her mother (Margaret)'s maiden name though I had wondered whether it might have been Eugene.... (A family member suggested that Elsie might have worked under the stage name of Eugene but that might just be guesswork). But I think that you may all have put paid to that theory! And re Melbourne: 1901 Census gives her birth place as Melbourne.
Re the details from the marriage certificates: on the Chandler marriage (Lambeth 29 Nov 1901) both parties are shown as living at 27 Holland Road, North Brixton; Elsie's age is 21 years (spinster) and her father is William Louis Leslie Evans (deceased) profession or rank Coach Builder (Master). On the Blore marriage (Eastbourne, 4 April 1916) she is shown as a widow, aged 36, and her father's name is shown as William Louis Leslie Evans, and rank or profession is Gentleman Deceased.
Sue, Debra: Olga was Elsie's daughter, born in St Petersburg when Elsie was quite young, so I think for 'social' reasons she was listed as Margaret's daughter. She was visiting her mother, with her Russian nurse, in 1901, and didn't come to live in England until she came to school in Eastbourne in about 1913 or so.
Debra: just read your last - that looks like a fit - thank you very much; that's got me through the biggest and longest-lasting brick wall.
Rootschat is amazing. Anything I can do to help anyone at all...?
Thank you all again - Kate