Josie looked up. Once she realizes the trick is coming out wrong, pretend that she intends to do it wrong, as a joke or to prove that magic is only trickery, not supernatural. Sometimes a superior magician will even botch a trick intentionally, to deflate a situation where she is thought to be practicing Black Magic. Anyway, it's a little to late for that. Like pulling a kitten out of a hat instead of a rabbit, then making the kitten float away.
Nothing comes to mind.
Resume her training in private, and find a new audience when she's ready. No, Forest Hill Elementary isn't much, but it's all I've got. Your own grandmother says that method is extremely dangerous and not recommended. If I was scared off by every 'extremely dangerous' warning I never would have done the 'Disappearing Car' trick on Principal Laquit's minivan. I rolled my eyes.