When Timmy was about to wish for a super bike, Cosmo and Wanda stopped him before he made the wish. Cosmo reminded him of this wish when trying to explain why Timmy should not wish for a super bike. According to the flashback that was shown, Super Kitty was so vicious that it scared the local dogs away. It then pounces on presumingly Timmy since he was running away with the dogs. What happened next is unknown as the flashback ended at that point, but it can be assumed that Super Kitty was unwished to prevent any further damage. If so it would have been most likely sent to Unwish Island due to its violent nature.