The level of ferritin for my daughter that age 14 years is 7.49 ng/ml in the time where she is taking iron supplement from 3 years . what's the solut?

Consider Specialist: 14 yr old on "iron supplement x 3 yrs", "ferritin = 7.49 ng/ml". Ferritin < 10 ng/ml indicates an absence of iron stores. This can result from many disease states, most commonly chronic blood loss (for ex. heavy menstrual bleeding), & chronic illnesses. No other lab data was given. Diagnosis can be challenging. See your doctor for further evaluation, consider referral to Hematology specialist.