she is outside the room. go outside and you have a cutscene with her then she runs off to do "errands *cough* traitor *cough* and she shows up again later with some more cutscenes later
Judging from her mental state (if you pay attention to what she says during conversations in both AC2 and ACB) and from reading the emails, saying that she is a traitor is far fetched at the very best.
Theres already a thread about this, widely believed its a glitch, she doesn't show up again till like sequence 8 at the end maybe later.
Just looked for that other thread, but i didn't find it...? I wanted to read it, because it sounds like an interesting bug.
You sure there's already one?
If yes, sorry for mentioning it ^^