Fischer was apprended in Belgrade and interned with her mother and her younger brother in the Vallegrande prison camp on the Croatian island of Korčula, then under the administration of Fascist Italy. She and her brother were allowed to assist her sick mother in the Split hospital. They were later granted permission to be transferred to Bologna. In 1943, following the outbreak of Italian Civil War, Fischer went on the hide with her family and adopted the cover surname "Venturi". She began to collaborate with the “Partito d’Azione” (a Resistance movement against the Nazi occupation) and met with Partisan Wanda Varotti and Massimo Massei.