Nadine picked up the stone and said "I wish I knew where this came from." But nothing happened, not that she thought it would. After all, she didn't know that it was a magic wishing stone.
This stone in particular had determined that Nadine wasn't the type of wisher it was hoping for. But the prudish Baptist girl could still be of use.
So instead of granting Nadine's wishes, the stone decided that it would grant the wishes of other people who make wishes about Nadine. But it would only grant the wishes that Nadine could hear. And while no one else would notice changes to Nadine and her life, Nadine herself would. There was nothing more satisfying than someone who was freaked out about a bunch of changes happening to them and not knowing how to stop it.
But who would be the first person to make a wish about Nadine, within hearing range of her?