Thinking back on how my niece wants to research the Holocaust, I don't think she's really grasped that it was a real thing. She doesn't want to read nonfiction reference books or biographies, and it actually took some struggle to get her to sit down and watch a program on the History Channel about it.
She has only expressed interest in fiction about the Holocaust. She's only read about refugees in hiding, minor details about the camps from outside observers, and as far as I know, none of those really touched upon the atrocities that had happened.
Maybe that's why she made the nut dolls and "Concentration Carton." Because she doesn't fully realize the true scope of it and has it written off as a "thing that happened to Jews."
Hell, when I brought up the fact that the Holocaust included others who were not Jewish (Roma, Polish, political dissidents, the disabled and mentally-ill, other races, those simply deemed as "unfit"), she dismissed them completely.
If she's going to be obsessed over it, she should do more research and learn more about it. Reading The Boy in the Striped Pajamas will not tell her all she needs to know.