In 1937 Grabhorn established her own imprint, the Jumbo Press, which she used as a vehicle for experimentation and artistic expression.

[2][3] Her best-known work for the Jumbo Press was the treatise A Typografic Discourse for the Distaff Side of Printing, a Book by Ladies (1937),[4] which was included in the compilation Bookmaking on the Distaff Side,[5] a collaborative feminist work by Grabhorn, Edna Beilenson, Bruce Rogers, and others.

Grabhorn also wrote, illustrated, and published via the Jumbo Press A Guide & Handbook for Amateurs of Printing (1937).

[6] Grabhorn founded the Colt Press (1938–1942) in San Francisco with William M. Roth and Jane Swinerton.

[7] Notable publications include their first, Lola Montez: The Mid-Victorian Bad Girl in California, by Oscar Lewis (1938);[8] Kamehameha, King of the Hawaiian Islands, by Marie Louise Burke (1939),[9] which was chosen as one of the fifty "Books of the Year" by the American Institute of Graphic Arts; and McTeague: A Story of San Francisco, by Frank Norris (1941).