dear user about your question i would like to tell you that chronic hedache with fatigue has many causes and simply we can reach the cause of your niece hedache by simple steps.... first cause of hedache is stress and anxiety and sleeping disorders and you should observe any emotional or psychological troubles your niece has as it is commonat this age.... second cause that we may role out is anemia and poor feeding because anemia cause severe fatigue and hedache and should be managed if present...... other cause of chronic hedache is visual disorders or photobia and my advice to you to refer to ophthalmology clinic to chech for any problems with eye... you shouldnot get worry of that and just follow these simple steps and try to relax your niece and give funny days to relieve of stress....... hope that helps