After Egwene arrives, she will begin the seige by using her abilities with Earth to block the harbors (she mentioned somewhere that she would have to test sisters for abilities with Earth before they reached Tar'Valon). She will bond Gawain, though I haven't decided yet whether he will come to her openly right away, or if he will be a snake in Eliada's basket for a while. We know that Messana is in the tower, and that Swain hid the horn of Valier somewhere there.

Mat will be heading to Tar'Valon, and Thom will have the letter with the names of the sisters who unlawfully genteled his nephew, and I can't think of a better time for it to be used. I think it is highly likely that Messana is Danelle, that brown who was restoring the library, and I also think that Swain hid the horn somewhere there.

When the confrontation between Egwene and Eliada comes, I think that Messana will come out in the open with the horn and gather the black ajah. She will attempt to blow the horn, and finding that it does not work, will battle the other aes'sadi for the control of the tower. This will lead to the bloodshed and the battle that Min saw in her viewing. That Egwene will win and gain control of the tower is certain, how and with what cost is the real question. I believe that she will kill Messana, destroy the black ajah, and recapture the horn. Along the way she could accuse Eliada of unlawful dealings with men who could channel, if Thom had shown her Moraine's letter. She could not deny it, since she had genteled men without giving them a trial, but everyone else would think that she had set up Logain as a false dragon. That alone would be enough to end her political career.

If she finds out about saidin being cleansed and if she could say that Caudensaine backed the claim up, the red ajah would be at her mercy being in danger of their ajah being disolved. If Egwene does kill Messana, the rest of the tower would not complain about her being the Armlyen.

Yes, I know this crazy and that there are a few holes, but I will try to fill them. Than Messana does not know that Mat already blew the horn is possible, since Forsaken do not always (meaning VERY rairly ) tell eachother anything. The second is that Eliada may realize what Egwene is trying to do and may say that she did not set up Logain as a false dragon. Two things may prevent this, one being that Eliada may still be in shock over the forsaken being loose, that she might not relize what Egwene is trying to do. The other is the possibility that Egwene has the tallent of creating the same effect as tav'eren (remember when Talmanes asked her if she was shure that she was not ta'veren too?).