She purchased a bungalow in the Ocean Park section of Santa Monica in the late 1930s, where she lived for the remainder of her life, although she traveled widely.
Her first major book, published in 1960, was Five California Architects, the first work to bring to the attention of a wide audience the works of pioneer California modernists Charles and Henry Greene, Irving Gill, Bernard Maybeck, and the Los Angeles-based Austrian emigre Rudolf Schindler.
This book was followed by others devoted to the Case Study Houses sponsored by Arts & Architecture, Schindler's fellow emigre Richard Neutra, and architects Craig Ellwood, Calvin C. Straub, among others.
McCoy's last work was an essay for the catalog of an exhibition on the Case Study Houses which was mounted by the Los Angeles Museum of Contemporary Art.
Her extensive collection of papers, slides, and photographs, are held by the Archives of American Art of the Smithsonian Institution.