The Forgotten Children

Percy Jackson wasn't only child of Poseidon born in the past two decades.There was one other, also destined to either doom or save the world,with two others at her side. Yes, her. It's about time the spotlight was taken off the male heroes.
Anyways,in order to protect her, Poseidon hides the child. But where? Where does she grow up,completely hidden,removed from the wars? Why,the underworld of course. And surprise, surprise,the other children of the prophecy are there too.

Oh,in this story,Annabeth and Piper died in the Giant War and Calypso was never found