Yes! I was thinking for the plot line: Sophie's human-sister Amy is a demigod who finds that out when she turns 12, but she hasn't told Sophie. Foster family goes to New York for a vacation plan and it fails. Amy stumbles upon Camp Half-Blood, where she finds out she's daughter of Demeter and becomes friends with Percy and friends. When the vacation is over she has to go back to San Diego, when 2 days later her parents get kidnapped and 1 week later Sophie and her friends welcomed her into the Lost Cities. When she get back to her house with her parents not in the Lost Cities anymore, her parents wanted to move into London where she find out about witches and wizards are real. She stumbles into Diagon Alley and finds Harry Potter and friends. Percy's mom is a witch. She died one year later... Estelle is a witch. She receives a letter to go to Hogwarts. She get sorted into Gryffindor. Harry has a long lost twin sister that is actually an elf. Her name is Ayla. Abilities: Hydrokinetic and Pyrokinetic. Amy, Estelle and Ayla meet because of a prophecy that tells them that Harry, Percy, and Sophie are in danger and that they're kidnapped by the Neverseen, some of the Dark Eaters, and some of the bad Titans. They recruit an army from all worlds and save them.