The Mystery of Harriet Potter

AU- Harry 'makes up' a twin sister when he is four, but she seems to get more real all the time. When Hogwarts letters come and Harriet gets one as well, Harry is even more confused. A trip to Gringotts with Hagrid exposes the deceit and manipulation behind Harriet's strange case, and brother and sister are able to attend Hogwarts together. But that is only the beginning...