Thinking that his life as a girl sounded too good to pass up (not only good for him, but also for others), Jon decided to go for it.
"I wish that I had been born as a girl," he said. And after the stone glowed, he saw that his body was now female, with girls clothes. Jennifer smiled, thinking that everything would be alright now.
But, of course, as long as the wishing stone was around, nothing would ever be "alright".