It will take 12-16 weeks for recovery. Give her protein and calcium supplements and proper diet to recover completely.
There will be stiffness due to the cast and immobility and once recovered she will be referred to a physiotherapist.
I have found out that each one varies on healing time. I was told 6 months for complete recovery and yet found myself getting a bone graft on my fibula 5 months after injury. I am 17 months post injury now and still having problems and am waiting to have hardware removed. I would strongly suggest physio the minute your mom is able.Also,D3,and vit.C and perhaps B12 if there is any hint of nerve damage. Good luck and speedy recovery