Just let her me and don't encourage to exercise and do anything to change the shape of her body. FWIW, my husband and I are regular exercisers and very in shape and no way would we tell our kids that it's ok to do a certain exercise just to get flat abs or whatever.
My kids play a lot of sports and any extra exercises that they want to do has to have a functional purpose, such as to improve in a certain sports skill, etc., and not for vanity purposes.
You are setting her on a destructive path of diets and self esteem issues if you she is only putting effort in certain exercises for vanity purposes and not for overall health, strength, and fitness goals.