Freiburgs disease

We have been told that my daughter has Freiburgs diease and it is very rare.
She is 13 and has not pain when walking or running with orthotics in he shoes.
However she does feel pain on the top of the foot when pressure is applied.
She has been off games for 9 weeks and the conditions doesn’t seem to have got better.
There is very little imformation on the internet – can you give me some idea of how long the problem wil last?