Sarah's second wish was granted to the person who was nearest to her, which in this case was Jon, who was currently in his mother's bedroom, opening her underwear drawer.
Sarah's wish caused Jon to want to be as accurate as possible, when making himself look as much like a woman as he could. So, he decided to take his time.
Unfortunately, this gave him a greater risk of being discovered by his mother. And she obviously wouldn't be too pleased at finding out that her son was dressing up in her clothes.
