Earlier, right after Sarah made the wish to change Karyn into James "Fatcock" Sutherland and Jon into Emilia "Buttz" Bermúdez, she realized that something must have gone wrong with her wishing, because Karyn (although being turned into a tall muscular black male porn star with a 15 inch cock) still had D-cup breasts and blond hair. That wasn't what Sarah had wished for and after several tries to fix the mistake and failing, she made a wish to have the power to make anything happen just by saying whatever she wanted to happen. Then she stated that Karyn (now James "Fatcock" Sutherland) didn't have breasts or long blond hair ... and that worked.
Then, she used her "verbal command" power again to change reality, by telling James and Emilia to perform sex acts that would change them mentally to the point where they wouldn't want to return to normal. And then, again using her "verbal command" power but not the stone, she told them where they lived and told them that they were going back home, and suddenly they were back home.
With that single wish, it was almost like Sarah had godlike powers. She didn't even really need the stone anymore. But she didn't want anyone else to get their hands on it. After all, she didn't want anyone else to have the same power she had.
