I think Mesaana is stronger than Nyneave - Egwene knows Nyneaves strength - she is also aware of Sharina's strength (who is potentially stronger than Nyneave) - for her to comment on Mesaana - and be in AWE -Mesaana must be considerably stronger "...someone appeared in the room with her. the newcomer wore black....darkness swirled around her...the effect was unnatural and impressive.. Egwene looked into the womans eyes..There was power to those eyes....Egwene appeared in her rooms, then raised her hand to her head, sitting down on the bed. Light, but THAT woman had been STRONG!! Read page 578 - this is when Eggy meets Mesaana for the first time - and its not Katerine in disguise - the disguise happens about 2 pages later. The first encounter is between Eggy and Messy - and boy Eggy was petrified -she didnt even dare fight - from her POV/narrative it actually reads "..why fight? She couldn't"