If you look at your own wrist, you'll probably see a small bump on the outside of your wrist. This is the bottom of the ulnar bone in your forearm. The bump is called the ulnar styloid process.
For someone with wrist rheumatoid arthritis (RA) this bump starts to break down. The tendons around it thin out so the bump is more obvious. What you are seeing actually has a special name: caput ulnae syndrome.
Other changes in the wrist from RA can contribute to this syndrome. For example when the bones in the wrist are affected by the arthritis, they can start to shift position. This is called subluxation. They may rotate and even dislocate or collapse.
Anything that changes the alignment of the wrist or joints around the ulnar styloid process can make it appear more prominent. Sometimes a surgeon will remove the bony bump. This isn't just for cosmetic reasons. Reconstruction of the bones, tendons, and joints can help relieve your grandmother's pain and improve the use of her wrist and hand.