It would not be right to have Arrow’s 100th episode without Katie and i has now been confirmed by Marc that Katie will be appearing in the four-way crossove event that will feature Arrow’s 100th episode. At this time we only known she will be a part of the Arrow part but could turn up in the other shows (Supergirl, Flash and legends of Tomorrow). Marc has said they the episode will be No flashpoint. No flashback. so I think we can rule out Laurel being there so will Black Siren make her way to team Arrow? or will we see a new version from Earth 3 coming to play?. They started shooting the episode yesterday (23th Sep) and will finish on October 7th. So Katie should soon be coming to Vancouver to film her parts for it.