This is still speculation based on a lot of assumption. I could just as easily say the lack of emotion was her poker face. The knife is to free Ollie's hands. And the very next words out of her mouth are going to be, "Oliver, what are you doing here?" Chances of that are slim since the show rarely takes the obvious maudlin route, but it's still as good any other guess. There's nothing wrong with speculating. The thing is, calling her an "evil assassin" is a big leap from suggesting she might be acting irrationally and instinctively under extreme physical and psychological duress.