Some more information that may help
I don't think she remarried as there is a grave at St Peters Church Cemetery Westleton Suffolk for Agnes Norah Anstruthers Lowick, with the dates 1888 to 1975. Details can be found at gravestonephotos.com.
Francis and Agnes had 2 daughters Eileen H b1916 and Katharine N b1918 both in Alexandria.
Eileen married Robert William Hamilton in Jerusalem in 1935, Katharine married Antony T Irvine in 1940 in Jerusalem. Antony Irvine was a Sqd Ldr in the RAF and died over Greece in 1941 their son James was born in 1941.