Who is Grandmother in The Boy in the Striped Pyjamas by John Boyne?

Grandmother is Bruno's paternal grandmother. A former singer, Grandmother loves being the center of attention. She is outspoken and opinionated, especially in terms of her son's position in the Nazi regime. Grandmother encourages and pretty much insists that her son resign from his position to no avail. Bruno is unhappy when Grandmother fails to visit the family at "Out-With".