Harriet Potter and the Mirror to Die For

Harriet Potter is nothing special- just a skinny girl who lives a perfectly miserable life with her abusive aunt, uncle, and ugly cousin Dudla. She dreams of miracles and change, but they are only fantasies. One day however, she receives a curious letter that changes her life forever. How could she have ever known that she was a legend in another world entirely? (Gender-swapped AU)