What if James Potter had a sister? A twin sister who was his complete opposite, but also his best friend. James' sister is of course a wizard. Her name is Aubrey Potter. Aubrey is a smart girl. She can figure out things faster then normal wizards.
Of course, her brother, the amazing Potter, is always known before Aubrey. Aubrey was nicer than James, but no one cared. They all liked James simply because of his looks and his troublesome ways. It doesn't bother Aubrey because she loves her brother.