Hello I had gone through your question very diligently and I can understand your concern sudden weight loss could be related to various factors like poor nutrition Indigestion or mal absorption Infection like TB or HIV or worm infestation metabolic disorder or hormonal imbalances I would advise you certain life style modifications and adoption of healthy food habits Have plenty of fresh fruits and vegetables Avoid spicy fried and junk food or carbonated drinks Have good amount of protein in your diet like egg, meat, fish and beans, pulses (dal) Have glass of milk during breakfast and supper sprouted grains pulses and nuts , soybeans are good source of protein Have lots of water and fruit juices exercise regularly like gymming cycling and swimming I would suggest you to follow above mentioned guidelines genuinely,she will definitely get healthy weight there are various homeopathic and ayurvedic medicines are there which increases appetite and subsequently weight increases. Hope you will find my response helpful and informative please feel free to ask for more clarification good luck