Hey doctors i wonder what is the best weight for a 15 years old ?! which she is 5'6"?!

Wide range: There is a wide range of normal for teens! Anywhere from 115 - 145 may be considered normal

Height ang weight: A basic rule of thumb is allow 100# for the first 5 feet then 5# per inch So her ideal body weight by this would be 130#

Health weight: Please see these growth charts provided by the Centers for Disease Control and Prevention. https://www.cdc.gov/growthcharts/clinical_charts.htm