Is it healthy and safe for a 15 year old girl (110lbs and 5"4') to be eating between 400 and 800 calories each day and exercising off 1000?

Anorexia: Absolutely not! this could cause severe electrolyte abnormalities and eventual cardiac arrest if continued for prolonged periods of time (this is what happened to karen carpenter). 110 lbs for a 5'4" person is already at the low end of normal weight. Most 15 year olds need at least 1300 calories per day and usually closer to 1500 calories per day.