My sister has severe pain and swelling on the inside of her ankle and she has not had any injury. She is 52 years old and works standing all day on concrete kitchen. Whatshould she do?

I think she . Needs to see a foot and ankle specialist. Without evaluating her ankle, she may have posterior tibial tendonitis. This is a common problem in that location. Having said that she should be seen in person for evaluation and definitive diagnosis.
Recommend evaluation. Swelling and pain to a localized region of a joint without known injury or trauma always warrants a formal physician evaluation. Work up may include vital signs, x-ray, blood work and aspiration of joint. Recommend formal evaluation by physician sooner than later in a case or swelling/pain in joint without injury/trauma.
Ankle pain. It's possible to have severe pain in the in side of your ankle after prolonged over use or after the development of posterior tibial dysfunction. This pain must be evaluated by a foot specialist or a podiatrist. She must rest her ankle and ice it for now. At the first time visit, x-rays will be taken with a complete examination.
Tendonitis. Sounds like tendonitis/inflammation of the tendon. More than likely it is the posterior tibial tendon.