Your doctors office or local health department has a weight chart that can give you a gauge of what the medical world thinks a person should be. Lets face it everyone is different so it is only a gauge. Ideally a 14 years old girl should eat well, be active and get good sleep and however her body reacts to that is how she should be. She should no way be skinny like the sickly looking models that the media shoves in our faces. Oh, yeah one more thing she should be is happy....