After several months of inpatient service in surgery and internal medicine at Little Company of Mary Hospital in a Chicago suburb, she completed a three-month post-qualification at the state psychiatric hospital in Chattahoochee, Florida (November 1959 and January 1960), obtaining a nursing license as a State Registered Nurse, which was valid throughout the U.S. Kellnhauser worked as a ward nurse, department nurse, head nurse, or deputy nursing director in the departments of oncology, psychiatry, surgery, and the intensive care unit at Florida State Hospital, Jackson Memorial Hospital, and Cedars Medical Center in Miami.