Hi
Welcome to the MedHelp forum!
Yes, iron deficiency is the commonest cause of hair loss. Even if your daughter has not started the cycle, she is in a growing age. Iron deficiency can be due to poor intake or poor absorption or due to hidden loss from bleeding as is seen in UTI and gut problems like IBS. The cause of anemia has to be found out by various blood tests. Iron replacement along with diet rich in iron and hemoglobin should be given.
Hair loss can also be due to dandruff, dermatitis, shampoos, oils, soaps, dust and dirt etc. I think you should discuss these possibilities with your doctor. It is difficult to comment beyond this without examining.
Please consult a hematologist to correct her iron deficiency. Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!