My very stubborn sister has rheumatoid arthritis. what can she do to treat?

Thats a long visit: First she needs to know that the disease is serious and can be deforming. But just as importantly she needs to know there are many medications to treat this disease and even change the course of the disease. She will say all meds have side effects but many can be avoided and watched for. Get her to rheumatologist possibly one she has a friend or relative who goes to and she may feel more at ease.

See an MD: She needs to see a rheumatologist. These specialists are best equipped to advise and manage her problem, assuming the diagnosis accurate. Unfortunately, if she doesn't want to go, there is little you can do.