“Late at night and without permission…”
Look, if you’re going to be doing dangerous chemistry in the household you might as well go all-out and cook up some meth or something (this is not a serious suggestion.) Or do like I keep thinking I’ll do whenever I find I need some acetone and oxidize isopropanol with bleach instead of going to the store and getting weird looks when I buy nail-polish remover. (Neither is this, though it probably could be done safely enough. One thing that stops me from trying it is the lack of a decent ventilation system as well as the ensuing distillation problem.)
Radios are boring. Does anyone even build a crystal radio these days, and what could you get on it besides religious broadcasting and sports? How about a homebrewed low-megahertz continuous wave NMR? Bonus points if the school administration freaks out because of the use of the other N-word. Not sure about the output, but there’s gotta be a way to do it, even with a strip chart. (More power to you if you can figure it out, because all I can think of would be to start looking at old physics and p. chem journals from the 50s.) Or a Beowulf cluster of X-Box 360s (or if you want to be cheap and boring, NESes or Commodore 64s or Apple IIs, though that would actually become pretty cool if you had enough of them.)
Does she have a brother? How about the old classic, “Is my brother dumber than a hamster?” Or maybe she can borrow inkleberry’s kid (who apparently thinks he is a hamster) and pit him against a real hamster.
Okay, for a real suggestion, the New Horizons launched for Pluto last week. Although it’s a demonstration project, how about an explanation of the slingshot manuver it’s going to take around Jupiter and some of the other stuff about the mission. Best of all, she can crib it all (remember, it’s not plagirisim if everything’s cited 
) from the website. Even better if you can find a way to model the gravitational effect.
I did one once comparing homemade bubble solution to store bought. I tested how big the average bubbles were (well, that’s the theory, I actually lied through my teeth about the results) by letting the bubble pop on construction paper and measuring the diameter of the watermark left.
An even better project idea would be to see how many of her peers lie about their projects or have their parents do the majority of the work. I’d love to see the results on that one.
-Mosquito
Thanks guys! There are some really great suggestions in here.
Emily Rosa was in the fourth grade when she debunked Therapeutic Touch in a simple blind test for her school science fair. Maybe your kid could test some other kind of pseudoscience idea, like dowsing, Ouija boards, astrology, etc. Maybe she could even become famous!