Was Amyco at the Darkfriend Social in the Prologue of the Great Hunt? We saw some of the effects Ishmael/Morridin was able to do to the mind of Bors/Carridin when he gets nothing more than a glimpse of Matt in Ebu Dar. That seemed much more invasive than the oath rod, and that was on a mere non-channeler.

It is quite possible the "weakness" Sheriam alludes to the wonder girls in the Great Hunt goes beyond being turned completely to the shadow by 13 Myrdrall and 13 channelers. As with compulsion (a one power method), the Shadows turning someone trick (possibly a true power method) could come with different levels of shall we say suggestiveness, and therefore have nothing to do with the oath rod.

My point is, its a failure of logic to assume that the Darkone controls all his servants the same. The forsaken seem to run to S.G. even when they know the punishment will be extreme for their blunders, because they know to not obey is much worse, even after your are dead. Amyco, a low level B.A., doesn't prove that the D.O. uses only the oath rod to gain his loyalties. As one of the top three B.A., Verin clearly could have been subjected to much worse and therefore not as free to get herself stilled as we think.