She is also known for her work defining the components of coenzyme A which was a part of the research that led to a Nobel Prize for Fritz Albert Lipmann.
[3] She went on to earn a Ph.D. from the University of Texas in 1945 where she worked on lactic acid bacteria and their conversion of acetate into lipids and steroidal material,[4] research which built upon Esmond Emerson Snell's earliest work that identified acetate as a key factor leading to reliable growth of microorganisms.
As Lipmann[12][13] and others have described,[14] Guirard examined this material and discovered that the vitamin pantothenic acid only appeared after extended enzymatic activity.
[16] Later, Kaplan detailed Guirard's experiments and noted her repeated investigations into the samples she received, and how it was only through her extended curiosity that she was able to identify the presence of pantothenic acid within conenzyme A.
[18] In 1953, Lipmann reviewed the chemistry and function of coenyzme A and he noted it was 'through [Guirard]'s skillful observations that pantothenic acid was detected in the coenzyme".