Gretel

From The Wiki In Striped Pyjamas

Bruno’s sister. She is 12 years old and is obsessed with dolls. She is a member of the Hitler Youth and has a crush on Lieutenant Kotler.She is known to Bruno as the "hopeless case".Gretel was mostly always at the top of her class. Later after Kolter left she swapped dolls for maps. Although at the start of the book she seems to hate Bruno , she actually loves him as she cried a lot after he 'disapeared'.