She didn't like the way she looked and asked you for a diet. I am concerned for her, and for the many other adolescents who have difficulty accepting their bodies. Too much emphasis is placed on physical perfection these days. Each time you exercise and gain strength, endurance and flexibility, you increase your well-being and develop muscle.
Busy kids are happier kids.
Stop checking the scale and keep an activity log instead. Your body is doing some very important development at this time. Check out videos on nutrition from the library. Be grateful that you enjoy activities. Do them to have fun, and not specifically to lose weight.