Éponine Thénardier foils her dad's scheme simply because she feels like it
Don’t let the movies and musicals fool you: in the novel version of Les Misérables, Éponine is less a self-sacrificing martyr and more of a hardened street urchin who fears neither pain nor death. When her father’s gang arrives at the house of Valjean and Cosette to rob them, Éponine tells them, straight-up, "This doesn’t suit me." There are six of them. They have weapons. Literally all she does is stand there and laugh at them, and they scatter. They’re like "LEAVE THE MEN TO THEIR OWN AFFAIRS, YOU SILLY GIRL," and she says, "There are six of you, what matters that to me? You are men. Well, I'm a woman. You don't frighten me."