I don't have any credits left at the moment, but I tried a search for 'Susannah' (no surname) born between 1904 and 1907 at (County) Fife and it is showing 5 matches (1 page).
Hopefully one of those might have a mother Evelyn. Then again, Susannah could have been born in another county ...
There is also one match for an Evelyn Clark (no 'E') married between 1901-1909 at Fife to a 'Bower' ??
You may have this information already, but Evelyn's occupation on her marriage certificate sounded interesting.
Is this her family at Dumfernline on the 1901 census, with father Joseph a travelling showman?
Name: Joseph Clark
Age: 40
Estimated birth year: abt 1861
Relationship: Head
Spouse's name : Susannah Clark
Gender: Male
Where born: England
Registration Number: 424
Registration district: Dunfermline
Civil Parish: Dunfermline
Town: Dunfermline
County: Fife
Address: Market Street Caravan
Occupation: Travelling Showman
ED: 5
Household schedule number: 154
Line: 8
Roll: CSSCT1901_134
Household Members: Name Age
Joseph Clark 40
Susannah Clark 40
Lillie Clark 17
Annie Clark 16
Evelyn Clark 12
William G Clark 2
John C Brian 16
All the best, Anne