Bruno introduces Gretel, his older sister, to the reader as a “Hopeless Case.” She is three years older than him and just entering adolescence when the family moves to Out-With. Gretel and Bruno bicker like typical siblings, and she deliberately belittles and excludes Bruno to make him feel like a child. He pesters her and takes every opportunity to prove her wrong. When the family moves to Out-With, Gretel brings all her dolls with her, and they become her best source of companionship. There are no other children at the house for Bruno or Gretel to play with, and so Gretel is left without peers for social interaction. When Bruno overhears Gretel talking to her dolls, he briefly considers that she might be going mad, but he realizes how lonely she must be without her friends. When Bruno accidentally mentions Shmuel to her, Gretel becomes jealous and offended that he found someone to play with and didn’t tell her. However, when Bruno lies and says Shmuel is his imaginary friend, Gretel claims she is too old for something that childish.

The one person with whom Gretel does socialize is Lieutenant Kotler. At nineteen, he is seven years her senior, but Gretel desperately wants him to see her as a peer and a romantic prospect. She is mortified when Bruno tells Kotler her age, and she does her best to keep common ground with Kotler by telling him she will be a teenager just like him in a few weeks. Her flirtation with Kotler never comes to anything, and, when he is transferred away from Out-With, she is once again left without companions. When he leaves, Gretel throws out all her dolls and replaces them with maps of Europe which she uses to track the progress of the war. Gretel does not have the resources for typical childhood experiences at Out-With, and so she tries to be an adult instead.

As Gretel and Bruno grow at Out-With, they come to appreciate each other more than they did in Berlin. The most notable moments in which Gretel and Bruno relate to each other are when they contemplate the people on the other side of the fence. Both children have an instinct that there is something wrong about the camp, even if they don’t understand what it is. That nameless sense of wrong brings Gretel and Bruno to be more vulnerable with each other and set aside their bickering. The more Gretel talks to Kotler, Herr Liszt, and Father, the less she is willing to address or admit that discomfort. She does not see the Jewish people up close, so she is more comfortable parroting the idea that they are not as human as she is.