The Secret Sister of Percy Jackson

Elle's life has been pretty harsh, her mother left on the side of the road when she was a kid and Elle's dad is apparently with this other family with another kid exactly Elle's age called Percy Jackson. And to top this proverbial cake Elle has had to join this group called the Clann to survive against the monsters, thats right monsters. Because Elle isn't exactly normal, well Elle is a Demi-god and her father is Poseidon- Earth shaker, storm bringer and father of horses. So lets just say Elle thinks this Jackson kid and his family has had it easy and she wants revenge for being cast to the side. But at the moment Elle has got a mission from the Clann at the moment infiltrate a high school and bring in all the demi-gods into the Clann.