The Half Blood Princess

Snape is left in charge of y/n potter, the twin sister of Harry Potter. Harry and y/n grow up in completely separate worlds, completely clueless to the fact that the other exists. Y/n is sheltered her whole life by her supposed dad. Until at the age of 13 she finally convinces him to allow her to attend Hogwarts. With the murderous serious black on the loose shape becomes increasingly overprotective of her, not even allowing her to stay in her dorm. When she finally meets her long-lost twin she develops debilitating head pain. For most of the school year, she is hospitalized, with vivid flashbacks of her mother planing her own death. In all the chaos she latches onto the only sorce of stability she can find. She develops feelings for her closest friend Draco Malfoy.