This sort of brainstorming is perfectly timed, and Hermione throws herself into it. She's also undeniably happy that, for once, Harry isn't fixating on Malfoy. They determine that Harry will try and corner Slughorn after their next lesson, an attempt Hermione thinks has a 0.01 chance of working. If this is what they think will work, why even ask her opinion? She laughs a little to herself. They're as stubborn as she is, when it comes down to it.