Miss Ranskill comes home

This 1946 novel (by the author of the Worzel Gummidge books) is about a woman who goes on a cruise and is swept overboard; she lives for three years on a desert island before being rescued by a destroyer in 1943. When she returns to England it seems to her to have gone mad: she cannot buy clothes without 'coupons', her friends are only interested in 'war work', and yet she is considered uncivilised if she walks barefoot or is late for meals.