How can a 11-year-old 120 pound girl lose weight?

you have to be as honest as you can but she may get mad at you but soon enough she'll realize that your only trying to help. If she is to heavy set than you can do it a little diffrently buy more nutritional foods and not as much fatty meats or junk food then make a family excersize plan like bikeride on Friday walk on Saturday and you'll eventually see a difference in not only your daughters health and weight but your whole family.