Demigod

It's when Roxy Carter, daughter of Poseidon gets on the hogwarts express, she knows her life has gone horribly wrong. She cannot perform the slightest bit of magic but though she has powers, everyone hates her. Trying to get through the school year is about as hard as breaking down a solid block of stone with a raindrop. But she vows she will carry on, at least until she's absolutely sure that can't be bothered to do anything.