Board Thread:Spoilers!/@comment-24934360-20140512191810/@comment-24950802-20140518020604

She didn't turn any guards into trolls, she simply killed the trolls from the bridge for being unable to kill Snow I guess. The whole thing doesn't really make sense, but it's the writers' attempt to make sure that the trolls stayed dead. Snow was responsible for them being bugged and crushed in 1.03. In 3.22, she didn't use the dust on them, and if they stayed in troll form and alive, that could have had repercussions for the future. So the writers did away with them some other way.