When Sam comes across a video of Charlie attacking a district attorney, Dean thinks she has returned from Oz to hunt on her own.
Charlie returns from Oz - Sam is scanning the internet for suspicious paranormal activity and comes across a video of Charlie beating up a district attorney. Dean suspects she's back from Oz and hunting on her own, assuming the district attorney must have been a demon. When they do find Charlie, they are shocked when she tells them why she really came back from Oz.