Here’s a site that could help you as far as if you are wanting to find a place to get your dog certified for this. Your dog’s temperament would be a big factor in certification consideration.
You might try calling the SPCA in your area and ask if there are any local therapy dog training sites as I am sure the org. listed above is not the only one doing it.

Hi what you need to do is to go to a vet and get a clean bill of health, all shots and papers that go with them. Make sure the shots have been given 2-3 weeks before you visit the elderly. Most nursing homes allow good dogs to come in and visit but they must have their rabies tag and papers too. I think that is a wonderful idea but another thot is to make sure that no one is allergic to dogs as that could be a fatal visit for an elderly as allergic reactions can be bad. Just some ideas and i hoped they help. I used to work as a nurse in a nursing home and we had people bring pets in all the time if they were clean bill of health and papers and rabies tags. A quick story that’s true just to tell you one lady brought in a puppy that was too little to have rabies shots yet and she had several residents holding it and playing with it. The puppy had rabies and everyone of the people who touched it had to have rabies shots. So there could be a little liability with it too. Anyway good luck and hope this helps.

Your dog first needs basic obedience training, then you can check the phone book for a therapy group for dogs in your area. Your dog will be tested - it’s like the canine good citizenship test, to make sure your dog’s suitable. They’re also looking for a good relationship between dog and handler. If your dog passes, she’ll get a photo ID done, and you can choose from the places who allow therapy dogs to go in.

No certification is really needed but what I would suggest to you is that you get a CGC (canine Good citizen) certificate for her.
This will show the staff at the nursing home that the dog can be trusted.
Good Luck and God Bless

Many places require that she passes the canine good citizen test. Hop on google and look for the nearest place that offers the class and test they will also have all the info on where to go and how to get involved once sge passes. Good Luck

Well, she has to take classes for this. I suggest asking the elderly home, because they all have different rules for this.