Grese volunteered to work in a concentration camp. In 1942, when she was 19 years old, she started working as a guard at Ravensbrück, a concentration camp for women. In March 1943, she was sent to work at Auschwitz-Birkenau. After a year, Grese was promoted to "Rapportführerin" - warden - at Bergen-Belsen. This was the second-highest rank that a woman could reach. In this job, she helped choose which prisoners would be killed in the concentration camp's gas chambers.