I found your great-aunt in the 1939 register as Violet E Davey married to Thomas W Davey (also a window cleaner) and her date of birth is 6 May 1902. Technically she was therefore 8, not 9, at the 1911 census but I've seen many cases of parents 'rounding up' ages so it's not really an issue.
Davey Household (2 People) 455 Harrow Road , Paddington, London, England
First name(s) Last name(s) DOB Sex Occupation Marital status Schedule Schedule Sub Number
Violet E Davey 06 May 1902 Female Power Machinist Married 116 2
Thomas W Davey 16 Mar 1901 Male Window Cleaner Married 116 1
Marriages Dec 1921
Davey Thomas W Driscoll Paddington 1a 158
Driscoll Violet E Davey Paddington 1a 158
However, like Ada, Violet does not appear to have had her birth registered.