Rice Krispy Treats have exactly three ingredients, set out fine, and are served at room temp. They are really easy to make and she can even shape them while they are still soft into balls and put a sucker stick in them to make Krispy Pops. You can do it with coco krispies or fruity pebbles.
I concur with brownies from a mix, there's also basic sugar cookies (the drop kind not the roll out kind), cinnamon rolls made with premade frozen bread dough that you thaw roll out and add butter, sugar and cinnamon. Roll it up and then cut it with some thread to make the rolls, bake and then you can teach her how to make powder sugar frosting from the recipe on the back of the box.