It might be good to do that, Kit. You shouldn't have to, as she shouldn't be forgetting your appointments. But the fact that she has a couple times in the past (or thought you had an appointment one week when you didn't) suggests it might be good to send her an email. You wouldn't need to word it at "Just reminding you of my appointment tomorrow" but could say something like "We should have plenty to talk about at my appointment tomorrow" or "looking forward to seeing you tomorrow" or however you'd want to word it.