and...

Mesaana sent Alviarin on a quest to determine what the Ajah heads are up to. That indicates strongly that Mesaana is not one of the Ajah heads. There is a possibility that Mesaana is playing head games with Alviarin again. I am inclined to believe that Mesaana is NOT one of the ajah heads though.

I would not rule out Norine. She was listed as being friendless by Alviarin in the same PoV where she thinks the same about Danelle. The main thing that makes me suspect her, though is Norine's venom toward Alviarin. Plus, we see that Mesaana is wearing a plain white dress in the prologue in tGS. This is more likely to be a dress that she normally wears, since she only expected there to be Demandred and Moridin, there. Neither one of which she needed to wear anything more impressive or to wear a disguise for.

Reading KoD made me very confident that Norine was Mesaana's alter ego. Now, though, I am not so sure. You could easily be right about Danelle. My main problem with that is Danelle dropped out of the story line early. Although, maybe that is evidence for her being Mesaana, since Mesaana probably prefers to work in the background through Alviarin.