As a Resistance worker in occupied France, Lundy began supplying forged official documents to escapees from the camp at Bazancourt and to Jewish families.[4][5] She assisted the Communist Marcel Nautré,[4] and others involved in the Possum network,[3] in avoiding detection by the authorities, as well as providing shelter at her brother Georges' farm for Free French fighters parachuted into the region.[3][6]
Lundy was arrested on 19 June 1944 in her classroom at Gionges and was interrogated by the Gestapo at Châlons-sur-Marne, where she was subsequently imprisoned.[4][5][6] During the interrogation, to protect her brothers and sister (René, Lucien, Georges and Berthe) who were also working for the resistance, she pretended to be an only child. From there she was taken to Romainville,[4] and, on 18 July 1944, was deported, first to Saarbrücken Neue Bremm,[5][6] and then to the Ravensbrück concentration camp (prisoner number 47360).[3][5][6] On 16 November of the same year, she was transferred to the Schlieben subcamp of Buchenwald.[3][5] Her sister Berthe was also imprisoned in Germany and her elder brother Lucien was interned at Auschwitz concentration camp;[3][7] they both survived, but her other brother, Georges, did not and was murdered at Auschwitz-Birkenau in 1945.[3][6]
Yvette Lundy was freed from Schlieben by the Red Army on 20[8] or 21[5] April 1945 and, after a march of some 200 kilometres to Halle, was flown back to France, arriving at le Bourget on 8 May 1945.[4]