Sadie was part of the Israeli forces, serving under Alter Tse'elon. She was Alter's only friend, and accompanied her on their mission to the United States to capture the last man, but turned against Alter when she tried to kill the male astronauts. Sadie is later seen presiding over Alter's court martial, only to be assassinated by the guards who are loyal to Alter. Alter is often seen feeling incredibly guilty about killing her, but that never stopped her from continuing her quest.
After Alter murdered Eliana, she tells the dead woman to tell Sadie "hello" for her.