I am sorry your baby was having this problem and I am glad she is doing better at this time.
Here is a great article on Legg Calve Perthe Disease:
http://www.ahtluvr.com/ahtleggperthes.html
While it is possible that the vet made a wrong diagnosis, it could be that she has the disease and it is just progressing slowly. Did the vet say how severe it was and when he thought she would need surgery? How long ago was she diagnosed with it? I think she should be x-rayed again to see how fast the disease is progressing and then follow the advise of the vet. This is something you don't want to wait until it is very serious before you take action. I read that children also get this and glucosamine can help. Please keep us updated on her prognosis.