How many calories should a 14 year old girl who weighs 108 pounds eat a day?

She shouldn't be worrying about calories because when you are 14 you are still GROWING which means 1500 to 2000 calories but not of junk food. Just follow the Asian food pyramid, plenty of dark greens limit meat and animal products and go for whole grain bread products. Believe me, your pre-frontal cortex will thank you!