Inside Out - S4-E17
Angel: All this time, it was you, wasn't it?
Cordelia: Took you long enough to figure it out. But nice turn with the Lorne bait. You know, there was a time I would have seen that one coming eons before it ever crossed your tiny little mind.
Angel: Because you're so clever.
Cordelia: On a scale of you to me? Pretty damn.
Continuity mistake: Right after Cordelia has her vision, Wesley goes to the whiteboard. In the "Case" column he writes "N.D.U.O." Underneath what looks like "CARYNSS" crossed out. But once they find out that it is a Prio Motu demon and Angel writes it on the whiteboard, "N.D.U.O." disappears even though Angel did not rub it off.
Trivia: In the opening credits there is a shot of a girl standing alone on the corner of a street. This was taken from the Buffy episode "Anne", when Buffy was staying in Los Angeles.
Answer: Everybody including Angel saw her. After helping them and then being left alone to talk to Angel, Cordelia says that the Powers That Be let her come back one more time to help them. After Angel gets a call saying that she died, he realises that it was her spirit that was helping them the entire time.