I heard from a doctor on the TV that it's a symptom of Rheumatic Arthritis.
there's also something called "Rheumatic fever" an "overkill" response of the immune system that follows to an infection.
she should see a Rheumatologist
it's actually "Rheumatoid arthritis (RA)"
It could just be hot flashes that happen to us old ladies. It is caused by fluctuating hormones. - I usually just drink some very cold ice water with a little potassium and it goes away. I hope it's not arthritis.
Hot flashes can be due to hormonal imbalances in females after menopause. If also can be due to Vitamin defeciency. Please get her blood sugar done too .