Life and career
McIlwraith graduated from McGill University in 1914 and became a reader and editor for Doubleday, Page and Company. She worked as an assistant to
Harry E. Maule (1886-1971), the editor of Doubleday's Short Stories magazine. In 1936, she became the editor of the magazine.  In 1937, Short Stories Inc purchased the magazine and McIlwrith continued as the editor.
In 1938, Short Stories Inc purchased Weird Tales magazine. The magazine's editor, Farnsworth Wright was in poor health and resigned as editor in 1940.  McIlwraith took over as full editor at this point and would remain editor until the magazine ceased publication in 1954. Under her editorship authors and artists such as Ray Bradbury and Hannes Bok first appeared in the magazine.