Melissa Joan Hart, who plays the yearbook girl, probably had one of the most entertaining parts in the whole movie, but she isn't credited for her part! I watched the end credits about four times, and she definitely isn't in there.
Kerry, I'm not saying that you are wrong, but it seems like her parts in the movie are too long to just be considered a cameo, although not being credited would suggest otherwise.
If you go to www.imdb.com (the greatest place for movie facts) they have a listing of every movie and actor/es. If you type in Melissa Joan Hart's name and then look at what she's been in, it lists her as the yearbook girl and says "uncredited" by the movie name. So, it was her, and she didn't get any credit for it.
Melissa Joan Hart does a lot of cameos, or uncredited roles. She is mostly in teen movies. For example, she was in "Not Another Teen Movie," and a few others. In this movie, she did have more of a speaking part, but all of her shots could have been done in less then a day, and I think she is uncredited because she probably didn't get paid to do it, she did it for fun or for a favor.
Sometimes actors take uncredited roles just because they don't want to be credited for the role. I've heard that Kathy Bates was not credited for her role in Rat Race. Sometimes directors don't take credit just because they don't like the final outcome of the project.