"Nothing," Hermione hissed at Ron, and her eyes were livid but there was something behind them that was her begging him to just drop it. Please, please drop it.
She turned back to Harry and added to what Ron had said. "We're in just as much danger at Hogwarts. Every time we leave the castle, because don't you think they'll come after us too? Whether or not you've been a self-sacrificing thick headed ... " She stopped herself and took a visible heavy breath, steadying herself, trying to keep her voice calm.
"We're in just as much danger if we're not with you. So we might as well be with you, helping. It's what we're meant to do." And by the time she got to that last bit, there wasn't anything but conviction in her voice.