My daughter is 4'4 and weighs 115 lbs. What can I do to help her gradually lose weight? I think her metabolism is extremely low.

Weight. Maintain a healthy diet and smaller portions. Exercise instead of TV. Fortunately she is still growing so maintaining her weight while she grows works well. Have your doctor involved and ensure she is otherwise well., all the best and maintain her good esteem.
Obesity program. Check with your pediatrician, they should be a local children's hospital that has a comprehehnsive obesity program. You are not looking to lose weight, more like stabilize and grow into body.