Sofia Fleiß grew up in Berlin. She married Isaak Stern in 1927 and they had two children, Philip and Hanna. The couple ran a leather goods store. After the 1938 November pogrom, the family business was appropriated, and the Sterns lost their livelihood. They tried to emigrate to Chile but were unable to do so. In July 1941, Isaak Stern was imprisoned in Sachsenhausen concentration camp, where he was murdered in 1942.
In January 1942, Sofia Stern and her children were deported to the Riga ghetto. After the ghetto was dissolved in November 1943, she lost contact to her son. Shortly later, Sofia and Hanna Stern were taken to Kaiserwald concentration camp. They had to perform forced labor in an external work detail. The forced laborer Zeligs Šmuļjans put Stern in contact with Jānis Lipke, who had already helped other prisoners. Lipke arranged Sofia and Hanna Stern’s escape from the camp and hid them on the Millers family’s farm near Dobele. They lived there with twelve other persecuted Jews until their liberation in October 1944. After the war, Sofia and Hanna Stern initially stayed in Riga. They emigrated to Israel in 1950.