Most nursing homes require the dog to have atleast their CGC (Canine Good Cititzen)To acheive that award your dog will have to know basic obedience and be very sociable. You will have to check in your area to see if any dog trainers are AKC qualified to do this test with you and your dog.
As I said above, that is what MOST nursing homes require, some require the dog to have their TDI (Therapy Dog International) But then again some just require your dog to have taken an obedience class.
Never let the fear of striking out keep you from playing the game!
There are special training classes your dog needs to go through to become a certified therapy dog. There are two (that I know of, maybe more) organizations that she can become certified through, TDI..Therapy dogs International, and Bright and Beautiful Therapy Dogs. Google them for a chapter in your area and inquire which training schools in your area are certified by them to conduct classes.