Six small meals may work better than confronting your daughter with large plates of food at meals. There are commercial products designed for just about any special diet. This is how your dietitian can help. If you add 500 calories a day to your daughter's diet, she will gain a pound a week. On is called Megase.
Some people also do better on a mild antidepressant to increase their appetites.
Talk to the doctor about this. In serious situations, you can offer tube feeding during the night to increase calorie absorption. New equipment and products make this a reasonable solution. This information is not intended to be a substitute for professional medical advice. You should not use this information to diagnose or treat a health problem or disease without consulting with a qualified healthcare provider.