Amy is pretty silly, because Tsutomu has already expressed that they would not be able to continue beyond this dragon boss with only 3 party members, so he still needs trustworthy party members like herself. Additionally, the guild leader is only temporarily replacing her and originally Tsutomu's plan was for himself, Garm and her, so clearly he thought they could win with her power even when it doesn't compare to Kamiyu's. That said, her reaction is exactly how I expected it to be from the moment Kamiyu showed up as a replacement. She's always had some confidence issues, so hopefully, Tsutomu puts her fears to rest now.