My daughter is 11yrs and weighs 52kg.can she diet at this age and if so what diet plan should she follow?

No diet: Don't subject your daughter to a diet. Instead transition the entire household to healthier food so she is not singled out. This includes ridding the house of processed foods like while flour breads, cakes, sugary cereals and drinks, ice cream, cookies, cake, pasta, white rice, chips, pretzels, fried foods, hot dogs, etc. Add lots of fruits, veggies, beans, nuts, seeds, whole grains, & wild salmon.