I find that I suspect Silviana as well. I am reminded of the fact that Mesaana made schools for corrupting children during the War of Power. Her taking on the position of Mistress of Novices in the Tower would put her in a position where she could corrupt the novices and Accepted there and deliver her 'brood' of channelers.

Of course, I'm open to all the posibilites including Tsutama or some random clerk or maid. I don't think there is enough proof to pin it on someone absolutely at this time.