After the German invasion of the Soviet Union, Melnikaitė along with other Komsomol members was evacuated to Russia where she took a job at a machine tool plant in Tyumen. In July 1942, she joined the Soviet Army (16th Rifle Division) and was sent to a saboteur school in Balakhna. In May 1943, she finished the studies and together with 35 other partisans (including two other women) were airlifted to the Rasony District in Belarus. From there, they needed to travel on foot to partisan headquarters in forests near . Melnikaitė and a few others were assigned to the native Zarasai where she joined the Soviet partisan group Kęstutis under the name of Ona Kuosaitė.