Monis was a Resistance fighter in the Free French Forces (
FFL) and the Fighting French Forces (
FFC) within the Robin-Buckmaster network created by and of which she was the secretary. She used her singing tour (song order and word changes) to inform her network. She was arrested on 22 June 1942 at 6, place du Combat in Paris, and sent to
Fresnes prison, then interned on 10 September 1942 at the Autun citadel in the
Saône-et-Loire department. She declared herself to be non-Jewish and tried in vain to obtain a Catholic baptism certificate. Still, the new director of the status of Jewish people (under the general commissariat for Jewish questions), Emile Boutmy, demanded her father's birth certificate, which was impossible to provide. As a result, Monis was classified as "100% Jewish", on 22 December 1943. She was sent to the
Drancy camp where she left 100 francs at the
Caisse des Dépôts et Consignation before being deported to Auschwitz by convoy no. 66 on 20 January 1944. She was 21 years old. She escaped the extermination after being recruited into the Auschwitz women's orchestra as a singer in the orchestra led by
Alma Rosé. There she met other French women, including and Fanny Ruback, who also survived. All the survivors were transferred on 31 October 1944 to the
Bergen-Belsen camp, where they arrived on 2 November 1944. The camp was liberated on 15 April 1945 by the
British army. Monis was repatriated by truck on 17 May 1945 to Paris. She obtained her certificate as part of the French Fighting Force with the rank of Lieutenant of the French Resistance. ==After the war==