When readers first meet Rivka in the concentration camp, she tries to reassure Hannah, Esther, and Shifre. She tells the others not to be afraid during the night because "any 'Choosing' is done during the day." By this, Rivka means that the concentration camp guards only choose people to take to the gas chambers during the day. She also tells the others that if they are alive in this moment, then "it is enough." By this, she means that they should appreciate every moment of life they have while they are still able to do so.

Readers soon discover that Rivka has been in the concentration camp for about one year and that during that time, both her parents, her brother, and her sister have all been taken to the gas chambers. Rivka is a young girl, about ten years of age, but because of the horrendous difficulties she has already endured, she is mature beyond her years. She tells the others that they must listen to her because she "knows the things [they] need to know in this place."

Despite losing her parents and two siblings and despite already having spent a year in the concentration camp, Rivka is still doggedly optimistic. She insists that God must be watching over them, because "God made the Devil, so God is here, too." Rivka tells the others how to stay alive in the concentration camp. She tells them which prisoners to avoid and which to approach. She tells them how to get medicine and where to hide when the Commandant enters the camp.

At the end of the book, when Hannah returns to her present time, she realizes that Aunt Eva is Rivka after recognizing the tattoo on her arm. Eva and her family members had changed their names upon moving to America.