Was Bruno's grandmother against the Nazis? If so, how was she not killed?

Nathalie, Bruno’s grandmother, was a singer and what we can see in the story is that she still loves to sing and art related events. Every year for Christmas, she organizes a play for the family where she and the kids participated. She hates the idea of the Nazis and the concentration camps. She was outspoken about that. When Father was named Commandant of “Out-With”, she was very angry and upset. Bruno’s Grandfather was proud, but she was irritated, offended by that. She knew what was happening in those concentration camps and the suffering of all who went there. When all the family was congratulating Father, she was thinking that probably she made a mistake while raising Father because that new uniform was more no reason to be proud but a statement of how low he has gone.
Being a critic of the Third Reich and their plans was a criminal offense. Most people would have been in trouble, but Grandmother was safe. Probably because her son was the Commandant of Auschwitz. If the people knew that his mother was against the plan it could have been a humiliation and probably cause outrage in the community. The events at those camps were military secret and nothing that could alter that order was going to be allowed.

Bruno's grandmother is deeply hostile towards the Nazis. She bravely expresses her utter loathing for them and their sadistic cruelty. Much of her ire is directed towards her grandson, Bruno's father. For him to take over as commandant of Auschwitz represents a source of abiding shame for his grandmother. She knows full well what goes on there, what horrors await those unfortunate enough to enter its gates.
Despite her very public condemnation of the Nazis, Bruno's grandmother seems never to get into any trouble with the authorities. Publicly criticizing the Nazis in any way was a serious criminal offense in the Third Reich, one that could lead to imprisonment or even death. One possible reason for the authorities leaving Bruno's grandmother alone is that arresting her would potentially cause quite a scandal. The last thing the Nazis would want is for it to get out that the commandant of Auschwitz's own grandmother was against the regime in any way. Also any publicity could reveal what the Nazis were up to at Auschwitz, something they wanted to keep secret.