Well My Niece Is 13 Years Old She Weighs About

Well my niece is 13 years old she weighs about 155 pounds she's about 5 foot 6 she suffers with knee pains in the joints and hip pains in the joints for one she does not like eating vegetables when the weather gets cold she hurts very much in her legs and hips they been taking her to the doctor and I can't actually find out what's wrong