In all fairness, she did have a few other things on her mind at the time. And there’s also the question of whether knowing that you can cast a Patronus would actually facilitate it: You still need a happy thought, and it’s debateable whether “I know I can do it” should count. So maybe that was just the part that Hermione didn’t understand.
Count me in as one who thought the third was by far superior to the first two. Of course, I’ve never read the books and have little interest in doing so, but what little interest there is has grown exclusively since the third. Both the first two left me feeling, well that was cute, but nothing I want to spend anymore time with.
The third is the only one I’d ever be interested in seeing again, and I agree with Malodorous that it’s the only one of the three that doesn’t rely on audience enthusiasm for the books, but actually tries (and succeeds, IMHO) to be a real movie.
I have to laugh at fans of books who can’t get over someone else’s vision of the book’s characters and settings being different than their own, and who also cannot get their pea-sized brains around the notion that a movie is functionally different from a book. No great movie adapation is ever a strict translation of the book, nor can it be.