"I wish Karyn looked like herself again and was regular-sized," said Jon with his fingers crossed. The rock glowed and... success! There was regular Karyn, still naked, but full-sized and her normal body (still with the blonde hair and enlarged breasts from the morning, however).
"Ohthankgod!" she blurted out, "But how...?"
"It didn't have to undo any wishes. You just wished to know what happened. You still do, the changes were just superficial. Like if I wished for a burger, that doesn't mean I can't then wish for a grilled cheese later."
"Fix me!" squeaked Sara from the tabletop.
"I said already," said Karyn, wrapping her fingers around the doll-sized woman, "Fuck you."
"I'm not sure I even can," said Jon, whose mind was actually racing to try and help her. You actually wished for these things to happen to you. I can't just undo them."
"You fixed your girlfriend!" sobbed Sara, obviously missing the point.
"She's not my girlfriend," said Jon, flustered, "And there's a big difference. Nobody said, 'I wish Karyn had the height and proportions of a porn-star Barbie doll. Wait, oh, fuck..."