You lived in a huge house. Your parents were rich, like...filthy rich. And yet they did not care about you one bit. You had grown up with Sam and dean, as you'd met them as a little girl. They'd saved you from a demon, and routinely checked up on you, calling you whenever they could. Demons seemed to flock to you, for some reason that Sam and dean couldn't figure out. That was until you mentioned seeing the "yellow eyed demon" at about 13. Since then, they'd been taking you along with them on hunts, scared to leave you alone, just in case.
Though you grew up rich, you fit in just fine. Perfectly, actually. You loved greasy food, snuggling up to the boys in the dirty motel beds, and most of all, Baby. You loved that car, possibly as much as dean. You quickly learned about the supernatural, and came to possess an eyebrow raising amount of skill within the field. You were an expert killer, hunter, and very intelligent. You were good at research, and a good balance between the two older boys. You were like a magnet for trouble, though.
After a tough day of gathering Intel on the demon you were hunting, you came back, to find dean at the kitchen table, giving you a look.