She first appears in the first novel of the series, The Lightning Thief.
Throughout the series she becomes close friends with Percy Jackson, later becoming his main love interest and girlfriend.
Percy finds out that there's another child to the elders... Not allowed to go due to the danger of the new prophecy.
Grover and Chloe go out in search for Hades daughter in hopes for answers to the prophecy, only to realise shes nothing like they expected her to be."A half-blood of the eldest gods Shall reach sixteen against all odds And see the world in endless sleep The hero's soul, cursed blade shall reap A single choice shall end his days Olympus to preserve or raze." Enderdura and her brother Nivis come to Camp Half-Blood after a vicious attack both being scarred by a hell hound sent to kill them. Wanting a bit of adventure they go on a quest with the trio.
Since she is a daughter of Athena, she was not physically born, but is a literal 'brain child', and was delivered to her father in a golden basket by Zephyr, the West Wind.