My 16 year old daughter has pneumonia for at least one week and has had complete loss of appetite. Any reason for this?

Pneumonia. Don't worry about a loss of appetite during illness. It will go away. Meanwhile that's way grandmas reccomend chicken soup. Your grandma is pretty smart after all.
Pneumonia. Yes, your daughter is sick. She doesn't want to eat. Give her the medicine your dr prescribed, give her light meals, soups, and fluidls. Everyone who is sick will lose a little weight, but given a little patience they will come back twice as good.