Hello there, Thank you for your question with HCM! You have to know that some kids have a very fast metabolism due to genetics. It also may be normal for her depending on how tall she is. However, when you want to increase the weight of your daughter, you need to focus on her diet. Try to increase the amount of protein, choose higher calorie foods and increase milk. Maybe add some chocolate syrup to the milk for calories. Foods that contain a high amount of protein include cheese, meats, nuts, peanut butter, tofu and yogurt. Try to introduce those protein rich foods in her diet and have her eat more frequently. Make sure she is taking a daily multivitamin so she gets all the nutrients her body needs. There is also specialized drinks for children that are picky eaters or have trouble gaining weight. Pediasure is one of the more popular supplements. Hopefully this advice is helpful. I just want to stress that her weight may be normal for her height. Try going to a website such as the one listed below. It is a good start to determine if she is truly underweight. Good luck and keep me posted!