The stone had glowed, of course, because Joanne had just made a wish--specifically a wish to know where the stone came from in the new reality.
In the new reality, Jon's grandfather did not give the stone to his grandson--there was no grandson in his family. Instead he gave it to his daughter--Jon's ex-mother.
Which was good, in a way. Jon's ex-mother was the one who had made the wish and remembered the old reality--she knew the stone was originally Jon's. So Joanne didn't have to worry that the owner of the stone in the new reality would come after her and try to take it.
"It's a magic stone," explained Joanne. "I can prove it." Proving it was easy, but how much of the story should she tell?
