My mom have rheumatoid arthritis and suffer from severe ankle pain only in the right leg, while walking. what is the solution ?

Depends on duration.: The most common cause of ankle pain, especially in a younger, active person, is a soft tissue injury such as a sprain. However, it is easy to rule out ra, especially if the pain has lasted many weeks. An x-ray will tell a lot, and you could follow that up with RA blood tests if suspicion persists.

See below: An ankle or compression brace for support may be helpful.

Also: If the arthritis is advanced, total ankle joint replacement is a great alternative to bracing or fusion. I have had great success with this type of patient utilizing the star ankle.

See your doctor: There are many possible treatment choices, and they might include ankle braces or ankle/foot orthoses, steroid injections may provide symptomatic relief. Balancing rest and activity in a way that does not overstress the ankle, physical therapy and/or surgery (such as an ankle joint implant or fusion) might be options to consider. Good luck!