I'm on the fence too ... but there certainly seems times when she would have to disguise herself as other than AS just to move about the Tower with freedom... given the Ajah tensions I have a difficult time seeing her moving around too much without trouble, obscure sister would be just as difficult to deal with as being a Sitter.

I do agree that Norine is a good candidate though, it's hard to say with any certainty if she's a better candidate than Danelle since neither have had a lot of on-screen time but IMO Danelle is the obvious choice which could as likely make her a red herring as the real deal... in short, I haven't a clue who Mesaana really is