In 1941, Stemmler was handed over to the Gestapo and transported to Ravensbrück concentration camp, where as a prisoner, she served as a nurse and saved the lives of two Czech prisoners. She remained until her transfer in 1943 to the camp at Auschwitz. Without regard for her own safety, Stemmler used her medical training to treat patients who were suffering from illness or had been subjected to medical experimentation by the Nazis. She was evacuated in 1945 as part of a death march from the camp and was eventually liberated in April by the Red Army. Stemmler began working at the Eberswalde Upper District Office in the Soviet occupation zone in August 1945. After two years, she began working at Landessender Potsdam editing women's content for the radio. Simultaneously, she served as a trustee for the sawmill in Biesenthal. In 1950, Stemmler began working at the Municipal Communication Archive in Schwielowsee and at the end of that year was asked by the Socialist Unity Party of Germany () to take over the chair of the . She accepted the appointment and was officially elected unanimously as the district administrator on 28 December 1950. Stemmler was the only woman ever to hold the chair on the council, as in 1952 an administrative reorganization dissolved the Zauch-Belziger District Council, replacing it with the Council of the District of Potsdam, for which she served as the inaugural chair. During her terms, she was known for her strict adherence to the party ideology. After a heart attack in 1953, she resigned the post as council chair. Though Stemmler retired from politics, she remained active in the East German Red Cross and worked as a secretary of the East German Writers' Association in Berlin until 1961. In November 1961, she was elected to serve a four year post on the town council of Kleinmachnow. Early in February 1962, she agreed to act as interim mayor for two months because Otto Bachmann, the elected mayor was ill. Her term as acting mayor was extended and she held the post until March 1963. Stemmler was honored with the Clara Zetkin Medal in 1966 and the following year received the silver Patriotic Order of Merit from East Germany. In 1967, at a ceremony held at the Zwinger Palace in Dresden, she was honored with the Florence Nightingale Medal for her service as a volunteer military nurse. Stemmler died on 8 May 1976 in Kleinmachnow, East Germany.