i was never told to walk a certain distance a day, but was told in no uncertain terms that the exercises were absolutely essential for a full and best possible recovery. i took it on myself to do lots of walking, round and round the garden and up and down the path at first, as i was terrified of developing a clot. i set myself a target of walking for 10 minutes every hour which i stuck to religeously. even when sitting down i would flex my leg and foot almost continually. i was on crutches, partial weight bearing for 6 weeks, then two sticks for another 6, then one stick. as squad says it depends on the individual and the implant used, and the surgeon.
having said all that, i believe the hospital in this instance are a bit remiss in not giving this lady more advice. it you are a non-medical person then you really have very little idea of what will or won't cause yourself harm, or the importance of doing or not doing certain things.