This is such a touchy subject, I don’t envy you. I would tread very carefully here, especially if she has issues with food and body image already. I agree with everyone that suggested that you and she find fun activities to do. Racquetball, Tennis, swimming, hiking, etc. I understand that you’re concerned for her health, but I really can’t see a way that you can approach her on the subject of what she eats without making her feel bad. Maybe when you’re out hiking or swimming you can pack a picnic lunch with things she likes that are healthy so that the option for fast food is not there.