Thereqs kindness, and then there`s forgetting the responsibilities of your job. The popcorn she gave him was fine, but letting her guard down enough the guy could hurt her or get her gun wasn`t (and she`d been doing that long before that final scene). It wasn`t definitive the guy honestly forgot or was faking (that was pretty much the whole point of the trail) but regardless, a great many killers come across as "lost" and nonthreatening. That`s how they lure their victims. A prison guard should ALWAYS keep that in mind, no matter how much empathy they`re feeling for the prisoner. So yeahz she was totally stupid.