Hello dear Welcome to Health care magic family . I have evaluated your query in depth . @ Sudden weight loss with decreased appetite can be from - low hemoglobin - pyrexia of unknown origin - various infections from bacteria , virus - thyroid , sugar level alterations - immunosuppression from HIV , Tuberculosis or other conditions - others . @ She needs intensive physical examination by expert physician , series of necessary evaluations in form of laboratory , x-ray , ultrasound tests . Hope this will help you definitely . Feel free to ask any future health related query anytime . Thanks for evaluating my answer thoroughly . Regards dear .