[6] As a teenager, Seibert is reported to have read biographies of famous scientists which inspired her interest in science.

Seibert did her undergraduate work at Goucher College in Baltimore,[5] graduating Phi Beta Kappa in 1918.

She was financed by the Porter Fellowship of the American Philosophical Society, an award that was competitive for both men and women.

It was subsequently adopted by the Food and Drug Administration, the National Institutes of Health, and various pharmaceutical firms.

[12] She was further recognized in 1962 with the John Elliot Memorial Award from the American Association of Blood Banks for her work on pyrogens.

[3] Seibert served as an instructor in pathology from 1924 to 1928 at the University of Chicago and was hired as an assistant professor in biochemistry in 1928.

In 1927, her younger sister Mabel moved to Chicago to live and work with her, employed variously as her secretary and her research assistant.

The previous tuberculin derivative, Koch's substance, had produced false negative results in tuberculosis tests since the 1890s because of impurities in the material.

[5] She developed methods for purifying a crystalline tuberculin derivative using filters of porous clay and nitric-acid treated cotton.

[3] She and her sister Mabel then moved to St. Petersburg, Florida, where Florence continued to research the possible relationships between bacteria and types of cancers, working with Mound Park Hospital[3] and with the Bay Pines V.A.