I've watched it over again. The woman she unmasked is the same woman standing in front of the class after they all get back from the exercise in the bush. She isn't a recruit.
I don't think Miranda is acting with the terrorists. It's too obvious. All the way through season 1, they kept giving us red herrings so we'd think that it was a particular person who was the terrorist and then it turned out to be someone who didn't even have shade cast on him through the whole season (which I predicted by the way). It's always the person you don't expect. If they're following the same format for season 2, it won't end up being Miranda. There'll be some sort of sub-plot we'll find out later that clears her as a suspect; even using Alex as a diversion tactic so the terrorists are focusing on her instead of something else. Remember the bit about "hiding in plain sight"? I'm certain that's relevant here somewhere.
On another note, I'm glad Alex is not wearing those damn heels anymore. All I could think as she was running is "are these magic heels? How are they not making a racket? How have they not heard her yet?" ha ha
Here's what I don't get though - why would she throw the body down into where the terrorists all are? Why wouldn't she dispose of the body somewhere hidden and continue surveilling or making a plan? It would at least buy her some time to get more intell. Surely throwing the body in there would be like waving a red flag at a bull because they now know she is still alive and it would be harder for her to blend in now.