The Lightning Thief
by Rick Riordan
Clarisse lives in cabin #5. Ares, God of War, is her dad. She is the resident bully at Camp Half-Blood. When she tries to "initiate" Percy into camp culture by sticking his head in a toilet, Percy is able to communicate with the water and use it against Clarisse. Later, she tries to corner Percy and to kick his butt on the Capture-the-Flag field, but Percy bests her again.