The writers usually have nothing to do with the promos and trailers, that's all on ABC. They don't have much material for the spin-off right now and probably just used scenes from ONCE proper to make the trailer look a little more epic and exciting. But I'd be shocked if we won't see Barbara in "OUAT in Wonderland" at all. As long as she's interested and not too busy with other projects, I'm sure the Queen of Hearts will indeed be a part of the pre-curse Wonderland flashbacks.
