If your mother is suffering from weight loss, and the cause of the weight loss is not known, then she needs to have it looked into by her health care
provider. They need to make sure certain diseases are not contributing to her weight loss, such as diabetes, cancer, or thyroid conditions.
Regarding her fall and hip fracture, this puts her at increased nutritional risk. To recover well, she needs to eat good proteins (chicken, fish, dairy) and have a balanced diet to heal properly.
You do not mention if she has memory problems in your question. Is she safe to live at home alone? Why has her eating habits become so poor? Can she provide herself with nutritional meals? I would speak with the Social Worker in the short term care unit to see if she would qualify for any assistance once she returns home. She may need more assistance now, especially since she fractured her hip. You could also look into meals on wheels, as they often provide free meals to seniors at home.