Gross was born in Zagreb to Jewish parents, Mavro and Ella Gross, on 22 May 1922. During World War II and the occupation of Yugoslavia, Gross and her parents hid out near Zagreb in the village of Drenje Brdovečko until 1943, when they were arrested by the Nazis. She and her mother were deported to the Ravensbrück concentration camp where they worked as forced laborers for "Siemens &amp; Halske AG" producing bombs. Her father was deported to Buchenwald. Gross's father and other members of her family perished during Holocaust; she and her mother, however, survived.