Kay looked at John when he told her about not going alone. She didn't plan on it so when Bane said he would go with her, she gave John the look of 'see, I won't be alone', but it wasn't working initially. She could see how light headed he was feeling and she could feel his weak state through their bond. "John, I need you to stay with Sam and Serena. You're in no fit state to be out there with me and if you come along I will be more worried about you and put myself in twice as much danger. Bane will be with me for backup. We got this...trust me to come back to you" She told him, placing a hand on his hand. "Please" she added. 

Sam watched her sister with John and she could see how genuine her affections were toward this man. Kay rarely cared about anyone, but this was true affection toward him. "if she says she can do this with Bane, then she can do this" Sam told him. She may not know about this magic world like the group in front of her did, but she knew her sister. She knew how resilient Kay was and if Kay survived for as long as she did on her own before finding John, then she trusted Kay could do this task.