Her name was Margaret Rock, also known as one of Knox’s “girls” in Cottage 3 at Bletchley Park, working alongside Mavis Lever.
In August 1940 Knox complained the sexist Civil Service grading system had misclassified Rock as a linguist or clerk rather than a cryptanalyst, which capped her pay regardless of what she actually did. It wasn’t just an advocacy for fair pay, it was also Knox saying the scare quote “professors” are just fancy titles and grades for men who were not doing any better work than the women.
Indeed, it was Rock who broke the Abwehr Enigma (variant G) with Knox and Lever in October 1941. Despite the significance of this feeding into the “Double Cross” system and the D-Day deception, Rock was never graded fairly in her lifetime. She left the GCHQ in 1963. 
