In John Boyne's novel The Boy in the Striped Pajamas, Gretel is the older sister of the story's main protagonist, Bruno, the nine-year-old German boy who innocently befriends a young Jewish concentration camp prisoner named Shmuel. Gretel, we are told, is three years older than Bruno, who is nine at the story's opening, thereby making his sister twelve-years-old. Typical of older sister-younger brother relationships, Bruno considers Gretel a constant source of irritation, repeatedly referring to her as a "Hopeless Case" who "caused nothing but trouble for him." Gretel is smart and pretty, but becomes smitten by a young German Army officer under her father's command, Lieutenant Kotler, who serves in Boyne's novel the role of the quintessential Nazi, obediently executing every command, no matter how vile.
While Gretel is the older of the two children, she is equally adversely affected by the family's move to Poland. Like Bruno, she is lonely, having been forced to leave her friends behind in Berlin, and is forced to console herself with her large collection of dolls. In Chapter Sixteen, however, Bruno observes a strange transformation in his sister. Gretel has placed all of her dolls in bags and began to decorate her room instead in a wartime motif, with maps adorning the walls and pins inserted to track the progress of the German Army. It is Gretel who enlightens Bruno on the nature of the facility for which their father is commander, explaining that the fence surrounding the facility is intended to keep the Jews isolated because "[t]hey can't mix with us."