I have found Edith Cowle in the 1881 Census with her Sister, Elizabeth Cowle, who was one of the Witnesses at the Marriage in 1888

it also looks like Edith has a TWIN Sister.

1881 Census
Thomas COWLE Head M 40 Isle of Man, England Carter
Catherine COWLE Wife M 40 Isle of Man, England
C. W. COWLE Son U 18 Isle of Man, England Apprentice Grocer
Jane COWLE Daughter U 12 Isle of Man, England Scholar
Edith COWLE Daughter U 12 Isle of Man, England Scholar
Elizabeth COWLE Daughter U 10 Liverpool, Lancashire, England Scholar
John COWLE Son U 7 Liverpool, Lancashire, England Scholar
Jessie COWLE Daughter U 4 Liverpool, Lancashire, England Scholar
Walter COWLE Son U 3 Liverpool, Lancashire, England Scholar
James SOOLEY Lodger U 23 Cleator Moor, Cumberland, England Police Constable

Dwelling19 Clarence Grove
Census Place Everton, Lancashire, England
Public Records Office ReferenceRG11 Piece / Folio3663 / 44 Page Number21

and I think this is William Cain 's Wife,

1881 Census
Ann CAIN Wife M 51 Castletown, Isle of Man (Mariners Wife)

Dwelling 18 Samuel St
Census Place Everton, Lancashire, England
Public Records Office Reference RG11 Piece / Folio 3664 / 18 Page Number 30

I am still not convinced that this isn't the right marriage,

in the 1911 Census John Cain states he has been married for 22 years,

why would he put that down if he wasn't married ?

Averil