After the outbreak of war, Haberer, who had been studying art and philosophy at Bordeaux, joined the Resistance, where she met her future husband, Lucien Hamelin. She became more active after witnessing the Vel' d'Hiv Roundup in 1942, and began sheltering Jews in her home. Along with Lucien, she was arrested in August 1943, but escaped deportation initially because she was pregnant. Lucien was sent to Buchenwald concentration camp, while she was held at the La Roquette Prisons. There she began writing and drawing, her theme being the daily life of the female prisoners. She also kept a diary, recording their experiences. In April 1944 she gave birth to a son in a Paris hospital. With help from Michèle Noyer, she escaped with the child and took refuge at the home of a nurse near Clairac in her home region.