With the stone still in her hand, she yelled "I wish I was here to stay! Oh no! NO!!" The stone glowed and suddenly she watched as a ghostly image of Jon was expelled from her body.
As a ghost, she was able to move from one body to the next, temporarily. But since she wished to stay, her spirit became trapped in one body. Apparently, since it was permanent, Jon's spirit couldn't stay inside her body, and so it was expelled.
Floating just a few feet away from her was Jon's ghost. And he looked mad. Really mad.
He floated towards the girl who stole and changed his body, and tried to grab the stone, but he was a ghost now, so his hand went right through it.
He had to get it back some other way, but that meant possessing someone's body. Who should he choose?