Born into a Jewish family in Vienna in 1920, Schwager fled Austria after the 1938 "annexation" and ended up in occupied France working with the resistance.
The young woman's highly dangerous job was to chat up German soldiers stationed in France and try to turn them against the Nazis.
Several others doing the same were arrested and sent to Auschwitz and other camps, and Schwager had some narrow escapes including when the Gestapo raided her Paris flat.
"I don't remember ever being afraid. The unfortunate ones who just hid ended up being deported anyway," Schwager told Profil magazine this year.
She returned to Vienna in 1945 to discover that almost all her entire family had been murdered. Her sick father had even been carried out of their home in his chair.
Schwager remained a committed communist all her life -- she was honorary president of the Austrian Communist Party -- and campaigned tirelessly for women's rights.
She remained active until the end, making a speech this January in Vienna during commemorations for the 70th anniversary of the liberation of Auschwitz.