I have three theories for this one. One is the conventional theory, the Seanchan. This seems the most likely just do to the overwhelming evidence and info about the court of the Nine Moons, etc... I also like the Tamyrlin's theory about the Seafolk. One point i have to add to this is in TSR, when Mat is playing cards with the Tearian Nobles, he jokes about chasing after some seafolk and they all laugh at him. Another one of RJ's clues perhaps... My third theory is the least likely, but i kind of like it. The First's of Mayene clain to be directly descended from Artur Hawkwing, if they are telling teh truth then Berelaine could be considered a Daughter of the Nine Moons...and she is always saying that she is so fond of Perrin and Rand that she wants to meet the third of the group.