No, no. I think it served a very important purpose. She was able to DO it. She can still channel, and I think they were trying to show us she wasn't stilled/burned out or dead and transferred into Lanfear's body (and there was much lamenting from the theory boards).

The trailer was shown in a much more symbolic way than what will mirror actual events in the book, I think. And the channeling burst may have been there for dramatic effect, but I REALLY, really doubt that Jason would not have included it in there for a reason.

On a whole, I think the trailer was fairly artful yet mysterious (much like Moiraine), and gave some valuable information without going into the details.

I did NOT like the actress who did the voice-over, though. Did not match the tone of Moiraine's voice/character at all, IMO.