KZ Ravensbrück (1942–1943) Grese was initially denied entry into Ravensbrück's training program. She met with Gebhardt's colleague and was instructed to come back when she turned eighteen, which was six months away. She did not return within the expected time frame; however, this was because she was hired to work at another dairy farm from March 1941 to June 1942. She completed the program in three weeks, after which she was given the title of . During her seven-month employment at the camp, where she received fifty-four
Reichsmarks per month, she was claimed to have excelled her superiors. Grese went to see her father Alfred in 1943, who had remarried in 1939 to a widow with four children of her own, Grese returned to Ravensbrück immediately following the incident (her final return home), and spent the rest of her time at the concentration camp overseeing work details until March 1943, when she was transferred to Auschwitz II-Birkenau.
KZ Auschwitz II-Birkenau (1943–1945) Grese was assigned to "Camp B" after arriving at Birkenau in March 1943, where she worked as a telephone operator in the office of a . She allegedly committed a violation while working on this assignment, prompting her to be transferred to oversee a (punishment detail). While she would claim during the Belsen trial that she only oversaw this section for two days, argued that Grese was in charge for seven months and was responsible for the deaths of at least thirty prisoners per day. Grese was assigned various duties within the camp over the next few months. In the autumn, she led a gardening squad before taking over as mail censor from
Elisabeth Volkenrath in December. Grese, who was 20 years old at the time, was promoted to , performing satisfactorily. In May 1944, Grese was given the authority to oversee "Camp C", which consisted of 31 huts and held approximately 30,000 Jewish women from Poland and Hungary. However, survivor
Helen Spitzer Tichauer revealed in her 1945 testimony that Grese was insufficiently qualified to command this section of Birkenau alone. She was assigned to work alongside
Luise Danz, a new transfer from the
Kraków-Płaszów concentration camp. Survivor Edith Trieger also claimed Grese punched and kicked prisoners who attempted to flee the selection parades. Grese frequently ordered prisoners to "make sport", which referred to strenuous punitive exercises. Survivor
Olga Lengyel made numerous claims about Grese's sexual relations with SS personnel and both male and female Jewish prisoners while at Birkenau. Grese allegedly had affairs with married physician
Josef Mengele and
Josef Kramer, but her relationship with the former ended when he discovered her illicit liaisons with women. Grese's sexual interactions with imprisoned Jewish women were
sadistic in nature and frequent, according to a prisoner who had been appointed as her maid. Survivor
Gisella Perl, who worked as a doctor at Birkenau, wrote in her own memoir that Grese experienced orgasmic pleasure while watching her operate on young women's breasts that had been cut open by Grese's whip and infected with lice or dirt, using only a knife and no anesthesia. Perl also stated that Grese would kick the young woman being operated on if her screams interfered with her arousal. Grese remained at Birkenau's "Camp C" until her brief transfer back to Ravensbrück on 18 January 1945, when all personnel were ordered to move westward due to the advance of Soviet forces.
KZ Bergen-Belsen (1945) Grese's final assignment was to Bergen-Belsen in early March 1945. During her three-and-a-half week tenure, she served as (labor service leader) and (commander of ). She was not supposed to be assigned to Bergen-Belsen because Kramer planned to transfer her to another camp once she arrived. During the Belsen trial,
Johanna Bormann testified that Grese and Hatzinger "were very close and regularly sneaked off secretly to have sex". Grese repeated the torturous and sadistic acts she committed at Birkenau in Bergen-Belsen. This included forcing prisoners to "make sport", which she justified during her trial because she believed the prisoners were "capable of partaking in such physical torment". ==Arrest and the Belsen trial==