In 1936 Mayo married a medical doctor, Richard Gainsborough. She was by then an established artist and even during the war, while helping her husband in his Sussex practice, her art production continued. In 1944 a book she wrote and illustrated, , The Story of Living Things and their Evolution, appeared. In 1948 she designed for her husband's magazine (he was retired by then) Art News and Review. They divorced in 1952 and she left England, and made a new home in Australia, and New Zealand, where she had family.
Eileen Mayo valued a naturalistic accuracy. Her cat pictures are amazing and also they often blend into an abstract edge. Some are below:
Here is an illustration she did for a poem by T. S. Eliot
The poem is from Old Possum's Book of Practical Cats, and we see the poet addressing a cat in her illustration.