What Karyn didn't know was that the Wiccan coven that Sue (and Jonnie) was in wasn't just silly nonsense. Sue was a real witch, although not an overly-powerful one. And using her powers, she figured out who Karyn was and, more importantly, where the little bitch lived. Soon, she'd have her lover back and Karyn would be sorry for ever taking her away from her.
Meanwhile, at her house, Karyn guided Jonnie inside, reassuring the bimbo girl that Sue knew all about the sleepover and was fine with it.