She'd been a bitch. She'd realized that. But this shouldn't be- wasn't- a class that they studied in. It was a class where they learned of the difference between life and death, and they found out how to make that difference.
But she couldn't. She couldn't teach them properly. So much for a school of magic. Even at Hogwarts she had to keep her powers under wraps, and just teach them theory, and teach them spells, but not be able to show them anything. The frustration she felt! It was immense, and it seemed that everything added to it. Little things which in normal circumstances would slide off her without her giving a damn were driving her insane. For instance, that Potions professor kept sneering at her in obvious disdain for her qualifications. She realized that the entire school did, but at least they were polite about it and saved it until her back was turned. She sighed, and turned back to the class.
"...and so having a deep and practiced knowledge of magic is clearly the first rule of combat in my opinion." Hermione finished off with a proud smile. It was one that Buffy easily recognized. Many mistook it for smugness; she knew that it was simply satisfaction from having put forth her viewpoint and spreading what she thought to be helpful information.
"Much as I value your opinion Miss Granger, I'm afraid you're incorrect. If no one else has a suggestion- no? - then it falls to me to tell you. Listen hard, and remember this for the rest of your life. Don't die."
She spent all her time imparting knowledge, which was so often ignored.