What caused Gerta's mother's death in the graphic novel, What the Night Sings?

Gerta's mother died in a fire in Köhn when Gerta was young, after a raid on the Jewish club she frequented. She had dark blonde hair and painted little watercolors. She and Klemens lived a life of artistic fulfilment together. As the novel progresses, Gerta has flashbacks of her mother practicing Judaism and finds these memories comforting. Her mother’s memory is an important part in Gerta’s embracing of her faith.