Margarete (Grete) Rönnfeldt worked as a maid for Lilli and Heinrich Ernsthaft in Berlin-Schöneberg in the 1920s, and looked after their son Harry. After her marriage, she lived with her family in Neuenhagen, outside Berlin. She remained in contact with her Jewish former employers, whose situation deteriorated steadily after 1933. At the end of February 1943, the now 18-year-old Harry had to go underground. Lilli Ernsthaft, who had to work as a secretary at the Jewish Hospital, turned to her former employee for help in March 1943. Rönnfeldt was prepared to take the boy into her home. She told her three young daughters that “Uncle Harry” was a war comrade of their father, but no one must find out about him.
Harry Ernsthaft spent most of this time in the basement. To make himself useful, he gave the girls piano lessons and helped with their homework. He stayed in Neuenhagen until their liberation. His parents survived at the Jewish Hospital.
Grete Rönnfeldt was posthumously honored as Righteous Among the Nations by the Israeli Holocaust memorial center Yad Vashem in 2003.