She cannot complete the solo phase of her flight training (at age 16) till she has that medical completed.
I'm not sure that's entirely accurate. If she were studying for an NPPL then a medical declaration by her GP would suffice for solo flight.
I understand the advice of don't pay for all that training until you know there is no medical obstruction, but I'd suggest that if you really want to fly, spend the money on flying not doctors, until you NEED to spend it on Doctors.