Gay Madelon - 1931

It must have existed because you can get it on amazon, they even have a picture of the cover:

I can't find much about Ethel Calvert Phillips, except that she was quite prolific and wrote children's books from the nineteen-teens through the 40s.
There is slightly more information on Ilsa Martha Bischoff (1901-1990); This Source says:

"Ilse Martha Bischoff was born on November 21, 1901 in New York City, to Adele Maria Timme Bischoff and Ernst Bischoff, founder of the Ernst Bischoff (pharmaceuticals) Company of Ivoryton, Connecticut.
From 1928 to 1946, Bischoff illustrated 12 books and wrote two novels about George Washington's Portraitist, Gilbert Stuart: Painter's Coach in 1943, and Proud Heritage in 1949. Her autobiography, Drive Slowly: Six Dogs, was published in 1953. She was also an avid collector of Meissen porcelain."