Hi Colin,

I also had a look on ScotlandsPeople at the index to the 1911 census.

I expanded the search to:
[They say] "You searched for: Surname: "clarke"; Surname Option: Variants; Forename: "Frances"; Forename Option: Variations; Se x: "Female"; Age From: 21; Age To: 27; Year: 1911;"

There were 7 "hits" which were:
No Year Surname Forename Se x Age District City/County GROS Data
1 1911 CLARK FRANCES F 23 KELVIN GLASGOW CITY/LANARK 644/13 030/00 004
2 1911 CLARK FRANCES F 27 MORNINGSIDE EDINBURGH CITY/MIDLOTHIAN 685/06 106/00 003
3 1911 CLARK FRANCES A F 21 GALSTON /AYR 593/00 009/00 008
4 1911 CLARK FRANCES E F 24 ST MACHAR ABERDEEN CITY/ABERDEEN 168/02 036/00 011
5 1911 CLARK FRANCES M F 21 PORTOBELLO EDINBURGH CITY/MIDLOTHIAN 685/07 021/00 002
6 1911 CLARK FRANCES MARY F 23 ST MACHAR ABERDEEN CITY/ABERDEEN 168/02 017/00 005
7 1911 CLARK FRANCES SIM F 25 ST GEORGE EDINBURGH CITY/MIDLOTHIAN 685/01 018/00 016

If her age should have been 23 or 24 there is no.1 as a possibility, with no.5 an outside chance?
No.2 too old? And the others have "wrong" second initials.

Sue