Amelia Winchester

It all started when she meet an angel, literally. Castiel and Amelia meet at age 7, and became inseparable. Kinda like Cas and Izzy were/are... But that dreadful day when she turned 16, Amelia collapsed from an inoperable brain tumor. Given a week to live, Amelia decides to agree to Isabelle possessing her.
And that is when her story begins.
Izzy and Am shared a co-dominate relationship, both in control of the body, living at peace. Castiel visiting them whenever, and even a little romance between them all.
It might help to mention, Izzy is the only child of Lucifer; Satan himself. Poor girl forced to fall from heaven because of her dad.
Plus, Amelia is the long-lost twin of Sam Winchester; Lucifer's Vessel.

LETS JUST SAY, IT ISNT EASY BEING AMELIA