There is an extremely high degree of probability that this ocurred off-screen, but we already know that Egwene has decreed that any woman who would be called Aes Sedai would need to swear the Oaths as well as the state of the Tower at the end of "The Gathering Storm" made it seem clear that all of the Aes Sedai currently in the Tower had sworn the traditional Oaths, proven themselves not of the Black Ajah or Darkfriends, and did so publicly so that there would be no questions.

Ironically, the questionable ones are now the independent Aes Sedai who stood off to the side during the whole struggle including members of Cadsuanes' retinue. Verin and Elza were not members of Cadsuanes' group, which leaves the possibility of other Black Ajah near her (and close to Nynaeve and Rand) open.

By the way, considering that no special mention was made giving a better clue as to Asmodeans' killer and etc, I think that RJ tends to leave certain information out and sometimes he does this for very important reasons.

Who knows? Perhaps Siuan will retire in the next book to marry Gareth Bryne?