"Give it to me! I'll do it!" Athena yelled, grabbing the stone from Zoe. "I wish Tiffany wasn't a vampire!" The stone glowed, granting her wish. But again, it wasn't granted the way the wisher wanted it.
Zoe never wished that the popular people would become vampires - just Goths. The vampire part was just an extreme caused by the entity in the stone, so it was possible to wish Tiffany to not be a vampire. But instead of just becoming a human again (a Goth human, specifically), she became something else. Something that might have been even worse than a vampire.
Tiffany became a ...