The Troubles For the Daughter of Poseidon

The war with Gaea's finally over and everything is back to normal at Camp-Halfblood with now Romans coming into the picture, but what happens when Percy gets an unexpected surprise from a family member(from his Father's side) who's lived on her own in South America training demigods that weren't able to arrive to Camp. Now she's come back with her friends seeking help from Chiron in searching for the one mother figure they've had their entire lives who's now been captured by an army of Cyclopes who are rising up against Poseidon. Also when he gets to know her she remembers nothing of her past and although doesn't care if she doesn't she overcomes the secrets of her unknown past and looks to the future with her friends and love interest. And although Percy is her brother will she be able to fully trust him with her deepest darkest secret that only her friends know about? Or will the Cyclopes succeed in isolating her from her friends and using her as a secret weapon?
Sometimes switches POV's please no hate comments and I know the descriptions confusing, but bear with me also give me feedback please and thank you 
Hope You Enjoy!