That is Charlotte Hope, playing Myranda. We don’t know who the character is really, but I doubt she is Myranda Royce based on her age, timing, and her appearance in the trailer. I think they borrowed the name for the minor character.
They’re definitely casting Daario, and we have very good reason to think we’ll see Ramsay. And of course Mance Rayder hasn’t been announced yet, so we should get more announcements.