Have you searched for Catherine in the 1939 Register, to glean where she was and what she was doing at the time? When did she marry? Do you have a copy of her marriage record? Did she have any secretarial training?
If your friend's story has some merit, Catherine may have been a clerk with the Women’s Auxiliary Territorial Service (ATS).
ADDED: Or she may have been a civilian secretary, like Brenda Hart. She was a Cabinet Office secretary during WW2, and the secretary to Winston Churchill’s chief of staff, General Hastings Ismay. As such, she had extraordinary access to Churchill and other world leaders. She also accompanied Churchill on a diplomatic mission to Russia and Germany to meet with Allied leaders after the war.
Brenda Hart wasn't a spy, but a Government worker who had a "ringside seat" to key decisions made by the Allied leaders during the last two years of WW2. Perhaps your friend's Catherine Fitzpatrick was working in a secretarial capacity similar to Brenda Hart?
This WDYTYR article provides guidance on WW2 service records and how to obtain them.
Note: Scroll to the
Women’s Second World War Army records section of the article.
https://www.whodoyouthinkyouaremagazine.com/tutorials/military/second-world-war-army-records/
