I guessed that a few senior level Sisters would know, but forgot Siuan still had access to the spy network.

But, honestly, I'm still not positive that Egwene knows anything about Cadsuane other than her name and general reputation. It would be like trying to explain the natural attributes of someone like Sorilea. She looked for Cadsuanes' name on the list because Siuan had mentioned it to her, and she was dotting all 'i's and crossing all 't's, especially since the Shadow has proven they could insert someone near her and Rand even on high alert.

I'm thinking that Cadsuane will die before meeting Egwene, but if they do meet, I think Cadsuane will end up being impressed with Egwene. While Cadsuane is important for the time they are in, I think RJ meant for Egwene's importance and reputation to far outstrip Cadsuane in the history books while Cads will end up as a footnote in Tower history.