"Keep telling yourself that, Sweet-cheeks. Whatever it takes to get you through the night, 'kay?" It just so happened that at the moment siding with the Winchesters benefited her more than siding with the demons. That could change.
Sam would be fine. He was a big boy. One Winchester at a time. Not even Meg had managed the art of being in two places at once. Besides, if Sam died he's just be brought back again, right? Didn't the boys have God's renewal and restoration service on speed dial or something?
She handed him the knife, bloody as it was, and pulled out her angel blade. Hopefully there wouldn't be that many more demons to deal with, she'd been pretty thorough on her way in. No such luck. As they rounded the corner there was the very familiar growls of very pissed off hellhounds. "...Run!"