Sophie's cooperation with the Nazis commences as soon as she is sent to Auschwitz. There, she is forced to sacrifice one child so the other can live. To save her son Jan, Sophie chooses to send her little daughter Ava to her death. Until the day of her suicide, Sophie is filled with unrelenting guilt for her part in her beloved daughter's death.
Shortly after Eva's death, Jan is sent to the Children's camp while Sophie (as a skilled Polish Catholic multi-linguist, typist, and translator) is sent to work among a stenographic pool of workers. In order to avoid the fate that awaits millions of Jews at Auschwitz, Sophie is forced to use her secretarial skills to facilitate communications between Nazi officers and leaders.
When she is transferred to work for Rudolph Hoss (the commandant of Auschwitz) at his private quarters, Sophie enjoys certain benefits. For example, she need only share her sleeping quarters in the basement of the Hoss home with a few other prisoners. Most importantly, despite the dampness of the basement and the presence of rodents, Sophie is spared (for a short time) the terrible smell of burning flesh. In order to keep clean (a luxury at Auschwitz for prisoners), she can also make use of the laundry facilities within the opulent home.
For food, she can rely on receiving daily servings of table scraps, leftover crusts of bread, as well as vegetable and fruit remnants from a pan. Sometimes, there is a pilfered can of sardines or a hunk of Polish sausage in the mix. Compared to the fare back at the women's camp, such a diet is a sumptuous luxury and a veritable banquet in terms of quantity and availability.
To enjoy such privileges, Sophie has to use her impeccable German shorthand and language skills to benefit the Nazi death camp machine. Her work is emotionally draining; yet, despite the disturbing contents of some of the letters she must write, Sophie knows that she cannot betray any semblance of outward displeasure about them. To do so would have been to invite death. Thus, Sophie must pen disturbing military letters with brutal efficacy and detachment, even if they discuss the systematic torture and ultimate fiery deaths of Greek Jews in the crematoriums.
Sophie cooperates with Hoss and even submits herself to his housekeeper's sexual attentions in order to protect her precarious position in the Hoss home. Knowing Hoss's hatred for homosexuals, Sophie cannot report her rape at the hands of Wilhelmine, the sexually-deprived housekeeper. Also, when asked to steal a radio from the Hoss home for the benefit of the Polish Resistance Movement, Sophie refuses to do so. Later, Sophie uses her privileged position to beg for her and Jan's freedom. Despite Sophie's flirtatious banter and flattering words, Hoss sees through her manipulations and refuses to help her. Sophie is driven to anguished distraction at Hoss's merciless refusal. Not long after Sophie's tragic episode with Hoss, the commandant is scheduled to be transferred to Berlin.
Before he leaves, he promises to let Sophie see Jan and to work to have Jan transferred into the Lebensborn program. During the war, the Lebensborn program was pioneered by Heinrich Himmler to encourage the mass births of blond-haired, blue-eyed children. These children were to be used to populate an Aryan nation based on Nazi conceptions of racial purity. (Read more about the Lebensborn program here.) Hoss never keeps his promise, though, and Sophie never sees her children again. The novel ends with Sophie's eventual suicide; she dies a tormented woman, filled with overwhelming guilt to the last moments of her life.
It is very important to understand that Styron develops Sophie's actions of cooperating with the Nazis as a way to highlight the lack of power that people like Sophie had. What she does is for survival, and not out of an active sense of choice.
One way in which Sophie cooperates with the Nazis is in her fundamental choice. When confronted with the choice of which child should die, she does cooperate with the Nazis. In a very sad sense, Sophie becomes part of the Nazi machinery of death because of her choice. She complies with the Nazi orders to kill. Styron develops her character with this guilt in mind. At the most critical moment of her life as a mother, she cooperates with the Nazis. Being forced to do so is one of the most stunning examples of Nazi cruelty. Sophie also cooperates with the Nazis in the attempt to save her son. While she works as the stenographer for Hoss, she tries to work with the Nazi establishment in order to see change. She wants Hoss to move Jan into the Lebensborn program. While he refuses her request, it is clear that this is another example where Sophie cooperates with the Nazis.