Probably Brandon and Harriet wanted to leave just a little bit of a wiggle room for the supporters of the other theories.
But why would she be listed a s ruthless killer? If we discount Asmo, we haven't see her anyone in the series IIRC, certainly nobody of notice.

Anyway, even without the new evidence in ToM I've always discounted the Slayer reason for one simple reason - as far as he knows, Asmo is an extremely strong channeller. So Slayer giving him a chance to see him and react before killing him is absolutely idiotic. Why risk if instead killing from behind with a dagger or an arrow? He certainly had no qualms about attacking Perrin from ambushes numerous times, even though this was a battle where Slayer expected to have an advantage due to his bigger experience with T'A'R.