It doesn't STOP him or anything. It just annoys him and he bats her away. And she stabbed him in the cheek, where his suit didn't cover him, plus he wasn't expecting her to do anything. She doesn't manage anything "Chris and Kara couldn't" but I still like the moment because it shows that Lois doesn't take shit and will defend herself. Also, it was nice to see her upset over Reactron hurting Chris and even Kara.