During the occupation of Paris, the Bal Tabarin was frequented by German officers; she performed there then.[2] Unknown to the Germans, she was Jewish, but she was still interned for several months in late 1940 as an enemy alien, because as a South African, she was a British citizen.[2] On her release, she returned to the Bal Tabarin and paired up with Frederic Apcar to form the dancing duo “Florence et Frederic”.[2] They became famous, appearing on stage with the likes of Edith Piaf and Maurice Chevalier, while Waren at the same time aided the French Resistance.[2][3] She hid fellow Jews in her apartment, helped Jews find their way from one safe house to the next, smuggled supplies and arms to the French Resistance, and, after a performance in Germany for French prisoners of war, collected letters prisoners had written to their relatives, which if discovered could have made her a prisoner.[2] In 1944, Frederic rented a house in the suburbs to hide her and several other Jewish performers after learning she was to be arrested.