Scarlett told Kitty a secret and made her promise to keep it to herself. Something told Scarlett that Kitty wouldn't be able to keep her mouth shut so she decided to spy on her to make sure that she wouldn't spill the beans. Nothing but Scarlett pressing her strong powerful hands against kitty's face will keep her quiet. Seems like if Scarlett wants to keep her secret safe, she's going to have to take matters into her own hands.