The Youngest Winchester(-Potter)

What if Harry James Potter, the Boy-Who-Lived, was raised by Dumbledore (read House Elves) while his twin sister, Adeline Lilith Potter, was left with the Dursleys. What happens to Dumbledore's carefully calculated plans when Adeline decides she wants nothing to do with them? When she is more Slytherin than his plans had ever taken into consideration? And what about her brother?