If it's RA then finger swelling is par for the course and better to get it off sooner rather than later in case it causes serious issues with circulation which could be dangerous. How soon can she get to a jeweller?
If she is still having issues and things become urgent then if there is a helpline for the rheumatology nurses at her hospital then they may have a idea as it's likely they will have come across it before.
I've given up on wearing rings, save maybe on a chain around my neck. I even find watches uncomfortable a lot of the time. I hope she gets it sorted soon, even the thought of a ring being on my fingers at the moment make me wince.
How is her RA treated at the moment and how well controlled? If she has any deformity of the joint, that could make matters more complicated.