Adam's sister, deeply obsessed with him since they shared a sexual encounter in his youth. She secretly warns Alice via letters, attempts to kill her to protect Adam, and is subsequently shot by Alice with a flare pistol during the cemetery climax.
Their sibling bond is a crucial foundation of the film's hidden history.
The plot identifies Deborah as Adam's sister, and Adam explains that he and his sister used to visit the cabin together.
Her covert warnings temporarily place her in an apparent alliance with Alice.
Deborah admits that she sent the warning messages to Alice because she wanted to protect her from Adam's violent rages.
Explore the full interactive character relationship map of Killing Me Softly