Geraldine Viswanathan is playing Val's assistant. Mind you, that doesn't prevent her from also being Songbird or anyone else. Considering how much I adore her work in Miracle Workers and Bad Education, I like to think she's more than just an assistant. I noticed she barely got to say anything at the Comic-Con panel and post-panel interviews, so perhaps they're being tight lipped about who she is really playing.
Either way, I didn't see her in the trailer.
Edit: I stand corrected. I just rewatched the trailer (which I'm surprised is still up!) and she briefly appears at the 2:50 mark, looking up at something.