Revekka Kositskaia was born into a Jewish family in the early 1920s. During the Winter War between the Soviet Union and Finland (December 1939-March 1940) she served as a surgeon apparently at a military hospital. On one occasion she succeeded in saving the leg of a Finnish soldier even though colleagues believed that only amputation was possible.
Immediately after the outbreak of war on June 22, 1941 Rebecca Kositskaia volunteered to join the Red Army. She was assigned to be the chief physician of a hospital train. Near the city of Novgorod the train was heavily bombed and its commander and its political commissar (politruk) were killed. This left Kositskaia in charge of both the medical personnel and the wounded. Boris Dairedzhiev, who was a close acquaintance of Rebecca Kositskaia and himself served in the Red Army, noted her bravery and devotion to duty:
"Revekka decided to cross the forest and swamps to get to a nearby railway line, from which they could reach the main line [that was under the control of Soviet troops]. They consisted of a group of about 300 invalids, including 40 seriously wounded people who had to be carried, moving eastward led through forests and swamps by 30 women. The whole way they were followed by Messerschmitts that fired machineguns at them from the air. [In a letter to Dairedzhiev] Revekka had written: 'They flew so low that we could clearly see the faces of those bastards. With such faces people chop wood or carry out some other mechanical work. With such faces they shot my wounded.' Only on the fifth day, after losing about 50 people who were killed in these attacks, did they meet up with some of our [Red Army] retreating units. The commander of a unit that was defending the branch line was struck silent when he saw this terrible procession. As if on signal, his fighters jumped out from cover to help the wounded. They took them by the hand like children and brought them to their dugouts. In the evening a train arrived from a nearby station. The wounded were sent to the rear. On the way the surgical nurse Putishcheva lost her mind from what she had experienced."
Later, probably after the battle of Stalingrad, she was assigned to be head of a hospital train. At that time she continued to perform operations and several times donated blood for transfusions.