I actually also think that Mesaana is Silviana, but unlike our speculative friend, I've laid out my reasons for said belief in the other thread.

In short:

1) Keeper and Mistress of Novices are positions of power, which the FS like.

2) Silviana was the only Tower AS seemingly unaffected by the tower split.

3) Mesaana figured that after Egwene was captured, she needed to give Egwene some power in the tower otherwise the rebellion would crumble.

4) She also promised that the tower would fight for the Shadow - she probably thinks that Egwene can be manipulated.

5) By swearing first on the Oath Rod, she put herself in the best position to word the Oaths in a way that allowed her to escape them. eg "I am not Black Ajah" rather than "I do not and have not served the Dark One".

6) My main reason: The Epilogue of tGS reads:
"... Was Mesaana still in the Tower?
If so, she somehow knew how to defeat the Oath Rod.
A soft knock came at her door. It cracked a moment later. "Mother?" Silviana asked."

I know literary foreshadowing when I see it.