What is the best way for a 14 year old girl to lose weight that is already in physical activity?

Eat healthy!

Cut down on empty calorie foods such as chocolate and stay away from fatty foods such as Pizza and burgers. Instead of these foods, try to consume nutritious foods such as fruits and vegetables. REMEMBER TO DRINK EIGHT GLASSES OF WATER A DAY. Drinking sufficient water will aid in your weight loss.

It is also helpful to keep a food diary so that you are aware of how many calories you have consumed. To find out how many calories you are allowed each day, calculate your BMI (just type in 'kids BMI calculator' on google.

I followed these instructions with 45 minute workout sessions, im 15 and dropped from 65kgs to 54kgs so it should work for you too.

Hope I helped :)

xoxo