HI, thanks for using healthcare magic
If there was no previous history of pain in the shoulder, you may want to consider taking her to see her doctor for an assessment to determine the cause.
It is possible , at her age, that it is related to arthritis
but there are other causes of shoulder pain
that she would need to be evaluated for.
In addition her doctor may be able to recommend analgesia that would be effective for you.Physiotherapy
may also be helpful for her to regain function of both her legs and shoulders.
I hope this helps