Magician No More (on permanent hold)

I've run out of ideas, feel free to steal what I've got. It's not much.

What if a young magician from the mid 1800s was transported to Hogwarts... in the Marauder's era? What if there were three a double seventh son -gifted with magic- her twin - an unlucky thirteenth child with an unusual knack for natural magic- and their best friend -someone who was raised like a pure-blood in a world where blood divisions didn't exist.