Granny Weatherwax's first appearance has a couple nice ones: having an epic duel with the headmaster to give Esk a distraction, and telling Esk's staff exactly what she'll do to it if it lets her die.
Note that, while reading the book, you could be forgiven for thinking at first that witch magic is mostly words and more words, with maybe a couple of mild real magic spells thrown in. No wonder Esk desperately longs for wizard magic. And then, the duel happens. Jaws may drop.
After having Esk be in the background or be dismissed for a lot of the book, it's nice to hear Esk confront a couple of student wizards:
You're wizards! Bloody well wizz!
...And, shortly after that, she manages to Borrow the mind of the Unseen University.