I don't have enough info here to make a certain identification, but I do have (from census records) a Mary E. Darwin born in 1879 -- is that too earlier to be your Mary Ethel Darwin? This Mary E. Darwin was the daughter of a William Darwin (born 1851) and Elvira Fare (born 1858); William Darwin's family we can trace back to Virginia in the 1740's via Tennessee (from which a large number of American Darwins migrated to Texas in the 19th century). Mary E. Darwin's siblings include Mabel, Maud, William Herbert, Clara, Iler, Nora, Ruth, Thomas Eugene, Milton, and Rayomnd. Do any of these names sound like your family? Let me know, and goo luck hunting!