There's another thread around here somewhere that records how Tilda Swinton says how surprised she is that her image appears in a trailer when, in fact, she's not in this movie at all. I don't know if she shot a scene that ended up on the cutting room floor, or if they just used some footage from Lion.
The couple-second image in the trailer gives the implication that what's going on is some kind of a summoning up of her spirit, which could be a corruption (and possibly a very bad corruption) of the point in Caspian where Nikabrik brings the witch and werewolf and attempts to get Caspian to agree to use black magic to summon the Witch back to defeat Miraz. That suggestion barely gets past the talking stage when a fight breaks out, so the summoning never gets off the ground. If the movie has a part where the summoning actually happens, it wouldn't be being true to the story there - especially if the girls are there when it happens.