The Kay Tracey series by "Frances K. Judd" was produced by the Stratemeyer Syndicate and published by Cupples & Leon beginning in 1934. This was the same year that the Syndicate introduced the Dana Girls series by "Carolyn Keene" who was billed as "The Author of Nancy Drew."
Both series were intended to continue the success established by the Nancy Drew series which had become the Stratemeyer Syndicate's best seller, out performing the boys' series for the first time in the Syndicate's history.
Although several volumes were ghostwritten by Mildred Wirt Benson from the Syndicate's outlines, she did not write all of the books. The first two volumes were written by Elizabeth M. Duffield Ward, a prolific Syndicate ghostwriter who worked on just over 70 manuscripts (compared with Wirt's 62). Her father, John W. Duffield, wrote 116 books for the Syndicate. The final four volumes of the series were written by Anna Perot Rose Wright. Mildred Wirt Benson wrote volumes 3-12 and 14 of the series based on the Cupples & Leon numbering scheme.
Volume 13, The Forbidden Tower, was written by Edward Stratemeyer's youngest daughter, Edna Camilla Stratemeyer Squier.
Although most histories of the Syndicate relate the role of Harriet Stratemeyer Adams, Edward's eldest, both daughters continued the company founded by their father. Edna and Harriet worked together to continue the Syndicate series and the Kay Tracey and Dana Girls were among the first new series the sisters established.
Edna left with her husband and child to move to Florida where she became an inactive partner. However, in the twelve years they worked together, Edna created about half of the outlines for the Syndicate volumes in the established and new series.
It is rather unusual that Edna wrote this volume because the earliest release for a book signed by Harriet is for the 1943 Bobbsey Twins book.
The first two scans below are authorship summaries prepared by Nancy Axelrad. They were found in the Beinecke Collection at Yale University. The third scan is the release for Forbidden Tower from NYPL.