Anna was waiting for Sam and Dean to arrive. She felt bad about what she had to do. Sam and Dean had saved her, and now she had to kill Sam. Dean, too, if he tried to get in the way. If. Of course he would. Yeah, Sam had made a huge mistake, but this wasn't punishment. This was saving the world. She almost thought Sam would welcome this chance at redemption. She knew the Wincheters' full story and knew of their self-sacrificing ways. She would explain the situation and kill him as painlessly as possible.