Hi and welcome, roughcut.
What was Gladys's surname? Or put another way, who did Ethel marry?
I can see Ethel's birth in 1886 as Ethel Annie, registered Rochford registration district, Essex.
It looks like her marriage in Ap/May/Jun 1903, Camberwell Surrey to either Frederick Rutherford or Stephen Pelling - which was it? Or have I got the wrong marriage altogether?
It would be worth you finding the family in 1911 census to see what name Gladys went under, her age, where she was born and any other info that might help find her birth.