In The Boy in the Striped Pajamas, Bruno's grandmother is not happy about her son, Bruno's father, and his new job as the commandant of Auschwitz. Once Bruno’s father gets this assignment, he wears his new commandant uniform to Christmas dinner with his parents. Bruno’s grandfather is "very proud of his son” when he sees the new uniform. However, Bruno notes that “Grandmother was the only one who seemed unimpressed.”
In fact, she is sad about Bruno’s father and looks at him “as if he were a huge disappointment to her.” She even tells him about her disappointment, saying,
"I wonder - is this where I went wrong with you, Ralf?' she said. “I wonder if all the performances I made you give as a boy led you to this. Dressing up like a puppet on a string ...
”Standing there in your uniform,” she continued, “as if it makes you something special. Not even caring what it means really. What it stands for.”
Bruno’s grandmother believes that her son's involvement in the Nazi party and its military have changed him in a negative way. This is in contrast to the views her husband holds. Bruno's grandfather is proud that his son has attained a high rank within the Nazi party. The grandfather feels that his son is helping Germany “reclaim her pride after all the great wrongs that were done to her.” He apparently does not see the Nazis the way the grandmother does; she recognizes that they are committing atrocities and believes it is wrong and immoral for her son to be one of them.
Specifically, she says that the Nazis are “doing ... terrible, terrible things.” She tells her son that it makes her ashamed to think of him as a member of a party that she feels is barbaric. Moreover, her son is not thinking for himself and being manipulated by the Nazis, she believes. This is why she characterizes him as "a puppet on a string" dancing to the Nazis' commands.
Before she leaves Bruno’s home after Christmas dinner, she turns to her son and yells one word—“Ashamed!”—to emphasize just how disappointed she is in him that he has become a high-ranking Nazi. She even tells him that it makes her sick to think about it and to realize what horrible things he and the other Nazis do.