What choice did Gretel make in The Boy in the Striped Pajamas?

In The Boy in the Striped Pajamas, Gretel is Bruno's twelve-year-old sister. The children are homeschooled by a private instructor who teaches them Nazi beliefs about the Holocaust and Adolf Hitler. At first Gretel is naive as to what is taking place during the Holocaust, but the teachings she and Bruno receive, along with her obsession with Lieutenant Kotler, inspire her to believe that she is superior to the Jewish people and that the Holocaust is just. In chapter 10, Bruno is curious as to why Gretel's behavior is shifting.

"I'm asking you, if we're not Jews, what were we instead?"
"We're the opposite," said Gretel, answering quickly and sounding a lot more satisfied with this answer. "Yes, that's it. We're the opposite."

At this moment, it is quite evident that Gretel is not only trying to convince Bruno that they are superior to the Jewish people, but she is also trying to convince herself. She has made the choice to support the Nazi party and the belief that she and her family are superior to their Jewish neighbors.