How did bianca disapear in Percy Jackson?

Bianca di Angelo disappears in "The Titan's Curse" after she joins the Hunters of Artemis, a group of immortal maidens. When she makes this choice, she leaves her brother Nico and the rest of her friends behind. Later in the story, she sacrifices herself to save her friends during a battle, ultimately leading to her tragic fate. Her disappearance is a significant moment that impacts the characters, especially Nico.