The Fate of the Dead

The second Emily Winchester saw the demon, she realized that this sure as hell wasn't a prank that her older brothers, Sam and Dean, were pulling. Unlike her brothers, Emily wasn't raised (or even taught) to hunt. From the time she was five to just before she saw her first demon, at 13 years old, she'd just been a kid trying to survive school with decent grades and friends, all the while trying to balance the fact that her dad and brothers were rarely home.
Dean convinced her that the family business was more important than anything else. That Dad was missing and they needed to find him. That he hunted monsters, like demons and spirits. In her mind, it was absolute bullshit, but Dean was completely serious, so Emily convinced herself to just go with it. Dean wasn't always sane, exactly, so Emily knew that she didn't necessarily have to believe him.
But just a few years later, Emily would learn just how terribly wrong she truly was.
***
Kalani Hilliker as Emily Winchester
Jensen Ackles as Dean Winchester
Jared Padalecki as Sam Winchester
Jeffery Dean Morgan as John Winchester
***
Book is recommended for a mature audience do to language, violence, possible sexual content, and (not so) occasional adult jokes. Read at your own risk. Spoilers ahead
***
Takes place 22 years after Mary Winchester is killed, as Dean and Emily (original character) find Sam.