In 1939, Steinhoff became a cook, married and had one child. In 1944, because of the Nazi call for new guards, she joined the camp staff at Stutthof. On 1 October 1944, she became a Blockleiterin in Stutthof women's camp SK-III. There, she took part in selections of prisoners to be sent to the gas chambers. On 31 October 1944, she was promoted to Second SS-Oberaufseherin and was assigned to the Danzig-Holm subcamp.
On 1 December 1944 she was reassigned to Bromberg-Ost female subcamp of Stutthof located in Bydgoszcz not far from Gdańsk. There on 25 January 1945, she received a medal for her loyalty and service to the Third Reich. She was devoted to her job in the camps and was known as a ruthless overseer. Shortly before the end of World War II, she fled the camp and went back home.