Likely not make any difference to your search, but Frances' address on the 1939 Register is 10 Lockington Ave., not Warleigh Ave. Four people are listed at this address, 1.Charles R. Mason. 2.Elizabeth B. Mason. 3.(Record officially closed), and 4.Frances D. Kemp/Jenkin. **Born 15/7/1917** Frances' occupation is listed as Domestic Service, but that doesn't automatically mean she is employed by the Mason family.
Good Luck with your search.
Regards, Dod.