“What are the possible methods of treatment for obesity?”

My recommendation, without knowing your daughter's history, is to find a physician who specializes in treating obesity in your area. Go to: https://obesitymedicine.org/find-obesity-treatment/ and you can find a bariatric doctor near you and they can review the options. Still the best method is for not only the child to eat healthy (meat, green vegetables and low carb fruit), but as a parent you need to do the same and set a good example.

Portion control and promoting healthy balanced diet and exercise regimen.