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 and with the Bay Pines V.A. Research Center. She continued to publish scientific papers until 1977. Theories relating bacteria to cancer continue to be controversial. In 1968, Seibert published her autobiography - "Pebbles on the Hill of a Scientist". Siebert received the Trudeau Medal from the National Tuberculosis Association in 1938, the Francis P. Garvan Medal from the American Chemical Society in 1942, and induction into the National Women's Hall of Fame in 1990. A historic marker was placed in her honor in Easton in 1993. She died at the Palm Springs Nursing Home in St. Petersburg, Florida on August 23, 1991. On November 15, 1993, a historical marker was dedicated at the location of her birth at 72 N. 2nd Street, Easton, PA.