Here's an improbable one. Mesaana is Toviene, the exiled Sitter for the Red Ajah who was summoned back to the Tower. Reasons: a) Being exiled for the ' vileness after the Aiel War (I presume she means the gentling of Owyn and others), that means she has not been seen or heard in the Tower for 20 years. Possible for her identity to be assumed by Messy. b) Elaida states that "unlike the other 2 Sitters, Toveine was not reduced to a nervous wreck. Why? Strength of character or simply just another person altogether.