Allen and his friend Jason.
"I wish I knew if I could change back to Jon," whispered Jenna.
"Not now," said a voice in her head.
"I wish I knew what I'd need to do to change back to Jon," she whispered.
The voice from the stone told her: "Wait until the end of the weekend."
Jenna groaned. "I wish I knew what's going on!"
The voice explained: "They wished that you would spend the rest of the weekend with them. You came to your campsite and met them after creating a fake bomb threat at your school. It was Friday. Today is Saturday. You can't change back until Sunday midnight."
"Leaving us already?" said Allen.
Jenna rushed forward to kiss him.
(Note: there's another hole in this story: Jon looked like a girl, but was still a boy. He didn't actually turn into a girl. Let's say that one of Allen's wishes did it as a side effect.)