Cause
It was only Meg's third day on the "job" and she was already bored. Castiel had passed out soon after the Winchester's had left his sorry ass to go do whatever the hell they normally do. Save the world or something like that. She didn't care what they were doing. Meg knew that as long as she was on the Winchester's side, she had a much higher chance of survival, and that by laying low, Crowley's goons wouldn't find her. Besides, she was tired of running.
Meg leaned back in her chair and attempted to entertain herself with the shitty gossip magazine she had picked up in the break room. Finally giving up on that, she stood up and walked over to the bed near Castiel's head. "Hey Clarence," she said as she poked him the face, "Any chance of you waking up soon?" She waited a bit, but received no reaction from the fallen angel. He was perfectly still, only broken by the steady rhythm of his light breathing, which was weird since as far as she knew, angels, like demons, didn't need to breathe.
Meg sighed and sat back down in her chair. It had been a rough two years since Big Daddy Lucifer had gotten trapped back in his cage by Gigantor the Talking Moose. She had been on the run from Crowley with a couple other Lucifer Loyalists for almost a year and a half when she ran into or rather trapped the Doofus Brothers again. Apparently Sammy Dearest had been pulled out of the pit without his usual charming morals and the Winchesters wanted her to get it back. She knew it'd be almost impossible, but they were agreeing to help her kill that son of a bitch Crowley in exchange.
Sadly things went sour when they were attacked by hell hounds. She and the other demons were left to deal with them while Tweedle-Dum and Tweedle-Bitchface ran off to kill the limey bastard who calls himself King of Hell. At least she got a smooch and an Angel Sword from the baby-faced angel. All the other loyalists were killed off by the hell hounds and Meg was captured by one of Crowley's henchmen for a game of "Torture the Demon". It had hurt like, well, hell, but eventually Antlers and Butch busted her out for their showdown with Crowley. They trapped and tortured him, but he broke out. Thankfully Castiel showed up right on time and burned the bastard's bones. Or so they'd thought.
She'd gotten the hell out as quickly as possible and had laid low. Right when she'd thought things were safe again, the monster kidnappings started up again, Castiel had made himself a god, and all hell had broken loose again. She was on the run again, until she was lucky enough to run into a desperate Dean and an amnesiac Castiel. She was able to convince Dean to remind Castiel who he really was so he could fix up poor little Sammy's broken brain. Cas transferred Sam's crazy into himself and they'd ended up were they were now.
"Well Castiel, it's just you and me now," she sighed, "I guess it's time I tell you about myself."