"From what I hear is she died on the quest with Percy, Zoe, and Thalia, and Grover, she chose to die against a huge robot named Talos, which was a prototype one though, she died and destroyed the robot and saved a statue from the junkyard for Nico, it was the only statue he didn't have, a statue of his father Hades. After that when he found out his sister died he blamed Percy, because he promised to bring her back safe, he runs away from camp and finds the entrance to the Labyrinth and escapes and still hates Percy, then Percy finds him and tells him to talk to Bianca as a ghost, he did so and Bianca told him that it wasn't the fault of Percy that she died, and that he wasn't mad at Percy, but her because she left him by himself in the World, and from that day on he is sort of normal but gets angry when his sister is mentioned because of his memory." I explain and take a deep breath.