I'd like to ask what 'game face' is:
Leaning forward in her chair, Penny said, louder: "Sit down and shut up."
Annabella, for the first time, seemed to notice that Penny wasn't in a mood to be trifled with. To be fair, Penny hadn't really put on her game face, as it were, until now. She had expected Annabella to react negatively, after all.