Fryderyka Mangel met her future husband Edmund Kessler in Rzeszow, when he moved to her home city after attending law school. They were married in 1937. Four years later, the young couple had to move into a ghetto, a part of the city where Jewish people were forced to live. They were separated in the summer of 1942, when Edmund was sent to the Janowska concentration camp. There he was beaten into unconsciousness several times and given hardly anything to eat. He escaped after three months, and was able to join Fryderyka. They first hid in the attic of a Pole who was sympathetic to their plight. Then a Ukrainian neighbor threatened to denounce them, and they had to move to a farm that had an underground bunker. The farm belonged to Wojciech and Katarzyna Kalwinski. Though their bunker measured only 5 by 7 meters, and the Kalwinskis were already hiding many people, they agreed to take in Fryderyka and Edmund. The Kesslers stayed there until they were liberated by the Soviet army on July 27, 1944.
In early 1945, the Kesslers returned to Rzeszow. They were forced to leave Fryderyka's hometown a few months later when a pogrom, an organized massacre of helpless Jewish people, broke out. They fled to Krakow, but left Poland for good after being threatened with another pogrom. This time, Fryderyka was seven months pregnant. The couple welcomed their daughter Renata to the family in Vienna, Austria. Edmund worked as administrator at the Rothschild Hospital in Vienna, which served as a way station for Jewish displaced persons. He later served as Chairman of the International Committee for Jewish Refugees. In 1952, the family immigrated to the United States. The Kalwinski family was honored by Yad Vashem as Righteous Among Nations in 1967.