She was Mary M in 1939
Maybe
CLARK, MARY MARGARET JOSEPHINE
Mother's Maiden Surname: CONNELL
GRO Reference: 1893 J Quarter in FULHAM Volume 01A Page 263
Had Walter James been married before?
Marriage
June 1892 Kensington 1a 336
Clark, Walter James
Connell, Margaret Josephine
Death
September 1899 Fulham 1a 263
Clark, Margaret Josephine
Age 32