Suddenly, in a blink of an eye, Jon became a girl.
"Oh, Jon. I'm so sorry. I didn't mean ..."
"Jon? Karyn, my name is Jen."
Jen didn't remember the previous reality, because Karyn had made her wish when Jon wasn't around. Meaning, Jon didn't hear the wish. So now, unless Karyn wished for Jen to remember (she'd have to get the stone, which was still back at Jen's house), Jon and Jon's life would be gone. Everyone, except for Karyn, never knew Jon. Instead, they knew Jen.
