Visible crew/equipment: When Angel is fighting the worm demon you can see a cameraman in one of the shots. (00:27:05)
Visible crew/equipment: When Angel is fighting the demon, you can see an obvious camera and two hands in the bottom right corner. (00:27:10)
Visible crew/equipment: When Angel is fighting the demon a cameraman is visible rising on the lower right. (00:27:13)
Revealing mistake: In the scene when Angel, a vampire, runs after the barman towards the end, after the barman has tried to pass on the demon to Kate and Angel stopped him, there is a mirror, and when Angel runs past it, he has a reflection. (00:38:20)
Continuity mistake: In the scene where Detective Lockely arrests Angel in the apartment, the window behind them shows that it's daytime. But when Angel jumps out the window, it's night time.
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.