Try something he'd definitely notice

Actually, maybe he just wasn't trying something noticeable enough. He could try making a wish that was so radical, he'd definitely notice. Either the wish worked, in which case he could undo it, or it didn't and he'd just have to try something else.

John pondered his options. What would... Aha. Now that, he would definitely notice.

He opened his mouth, and spoke;

"I'm a sexy woman", she said, the truth flowing easily from her mouth.

Jane looked down, a hand brushing her long hair out of her eyes as she did so. Her gaze travelled past her bountiful bosom, moving past her flat stomach to the gap between her feminine thighs. Everything was just the same as before.

She couldn't help but feel somewhat disappointed. It could just be that the power didn't work on her, or maybe that it didn't work at all. Or maybe she was just being stupid or something.