After Piłsudski's death in 1935, she co-founded the Belweder Museum, where she remained in a management role until September 1939. Her spare time was devoted to other military activities. In 1938 she became treasurer of the Federation of Polish Associations of the Defenders of the Homeland. World War II Soon after the outbreak of World War II in September 1939, Gertz was one of the first women to join the resistance movement, Service for Poland's Victory (Służba Zwycięstwu Polski - SZP), operating under the code name "Lena". She organized clandestine communications, acted as courier, and was assistant to the divisional commander, Stanisław Kozarski. In April 1942 Gertz was ordered to create and command a new unit Dywersja i Sabotaż Kobiet - "oddział Dysk" (Women's Diversion and Sabotage unit), as part of the Kedyw. Its members carried out attacks on German military personnel, airfields, trains and bridges. Gertz seems to have been sceptical about the planned Warsaw Uprising, and prohibited members of her group from taking part, though many did so anyway. She was promoted to the rank of major in September 1944. Captured after the Uprising, still known as Major Kazik, Gertz was held as a prisoner-of-war and recognised by the Germans as commandant of 2,000 other female fighters who had survived. She passed through camps at Ożarów, Lamsdorf and Mühlberg, and finally in late 1944 arrived at Molsdorf, all the while retaining command and respect among her fellow POWs. On 5 April 1945 the POWs of Molsdorf were marched to nearby Blankenhain before finally being liberated on 13 May 1945 by troops of the U.S. 89th Infantry Division. Post-war life As part of allied Polish forces in Germany under British command, Gertz arrived with them in the United Kingdom, returning to Europe after the German surrender to serve as Inspector for Women Home Army Soldiers. She travelled throughout Germany and Italy in search of displaced Polish women. From May 1946 until February 1949 she was part of the Polish Resettlement Corps, serving as Inspector of Women Soldiers in the north of England. Her task was to prepare them for civilian life in Britain. After demobilisation Gertz worked in a canteen until her death from cancer on 10 November 1958. Her funeral was attended by many veterans, including Aleksandra Piłsudska, and Generals Michał Karaszewicz-Tokarzewski and Tadeusz Bór-Komorowski. In 1960 her ashes were taken to Poland and interred at the Powązki