The 1939 Register gives her birthdate as 6 June 1908 which is just 9 days before the marriage of her mother Lily Blanch Nicholas to Thomas Abraham Stephens. It would be nice to confirm her birth date from the death register but I been unable to find any record of her death. I found her mother in the 1921 census, but she was not living with the family. She married Harold Clifford Dorrington at Tidenham, Glos on 1 Feb 1930 and on the marriage certificate she says her father is Thomas Stephens, but one has to be a bit suspicious as she was in the Workhouse in the 1911 Census and still not with the family in the 1921 Census.Harold Clifford Dorrington was born on 8 Mar 1908 and died in 1988 in the Newport, Monmothshire Registration District. There is a birth of a Catherine Stephens in the third quarter of 1908 in the Merthyr Tydfil Registration District which is a possibility.

By the way I found all this information on Ancestry.