The issue is simple: how could she maintain obedience when she will be showing weakness in front of her minions not once but twice. Furthermore, if any of the Black Ajah saw that collar (keeping in mind that many of them actually know what an a'dam does and may be able to recognize it), they would realize that she is entirely under their control. This is an organization full of evil people - trust is not something that they practice that often, and we know from the way the a'dam works, that you may very well be unable to draw upon the will necessary to destroy the one who holds your leash. Perhaps this weakened will would be enough to guarantee your destruction should you be trapped in a nightmare or their particular dream. From all descriptions we have received, being leashed is a draining experience and not something that keeps your willpower and sense of self (extremely important factors when manipulating T'A'R) intact.



Yet Egwene was completely unable to even initiate the attempt, nor could the Aes Sedai or Windfinders, all capable women of above average intelligence, figure out a way to remove the collars.

It may seem easy to us, as the readers, but I doubt if the collar were real, any one of us could figure out how it clasped, based upon the description of it we've gotten.