There is a marriage in Winchcombe of a Kathleen M BOX and a John A JOHNSON in 1930 which appears to be a reasonable fit.
This couple is living in Colerne, near Chippenham, in 1939 with one child. Her birth date was given as 9 Feb 1904 which which is slightly inconsistent with Kathleen's birth registration in Q1 1903. That said, it does seem unlikely that two Kathleen M BOXs would co-exist near Winchcombe.
2 Apr 1911
Laverton, Broadway, Worcestershire, England
13 Jan 1918
Place of death recorded as East Africa, but most likely Dar es Salaam.
Dar es Salaam, Dar es Salaam, Tanzania
Shipston on Stour, Warwickshire
29 Sep 1939
High Street, Colerne, Chippenham, Wiltshire, England
18 Jun 1977
15 Kings Road, Evesham, Worcestershire, England
Taunton Deane R.D., Somerset
West Oxfordshire R.D., Oxfordshire
Documented age, Calculated age, Estimated age>