How is she evil: They clearly didn't stand a chance. It wasn't about protecting herself. She didn't fear, they might bring reinforcements. She was angered in the beginning and genuinely surprised humans die so fast, but after she noticed that, she didn't stop. She didn't even stop when they were retreating. She had the means to capture at least some of them, with threat manipulation, after their formation broke down. She likes the EXPs she got from slaughtering them. And she was slaughtering them. Not just killing them, deadening them or doing them away, that was slaughter. From our human POV that qualifies as evil.