if the molar is decaying, it is best to get it out by the dentist and not wait for it to fall of on its own.
sometimes, if the infection runs deep, it could affect the roots deep inside, and cause severe pain and more infection. do visit a dentist ASAP and also show your kid why it is so important to take good care of teeth and gums. also cut down on sweet intake and make sure she brushes twice a day