Yeah, it's dangerous, but the best thing to do is get her active. My mom kept things around our house like badminton kits, kickball, baseball, bikes (even an extra one for when we had company) and she would get the neighborhood kids over to play with us. Back then we liked going outside to play. Now, they've taken activities out of the elementary schools, and sometimes kids don't even get recess outside (remember recess!).
But one thing I know the forbidden food thing doesn't work, it does something strange to girls. They have to decide. Parents have to make the choice of healthy foods being available in the house and not put kids on diets unless they have allergies or an illness.
I knew too many girls in college with eating disorders that started when they were children.
I started making choices that were right for me when I was older. And I get food shamed a lot. So, it's an ongoing thing.