Is a 17 year old girl who is 5'6''-5'7'' and weighs 141 pounds overweight?

It depends on your body type. If you are thin framed and have very little muscle mass, you could be considered overweight. However, if you are larger boned and have a lot of muscle, you could also be considered at the low end of your healthy weight range. Muscle weighs far more than fat and since most American women are considered sedentary, it is assumed they dont have significant muscle content. The Rush University Medical Center chart, which does not take frame size into consideration, puts a woman who is 5'6" between 117 and 143 pounds, which suggests you are not overweight.