As a long term hot flash sufferer, I can tell you that nothing works except estrogen. Can she get bio identical? I am your mom's age but have been suffering with these since I was in my 20's due to surgery.
They are miserable but low estrogen is better than no estrogen. A time for lots of fats in the diet if she is thin, this helps her store her estrogen for years to come.
If she has an outstanding healthy diet, this is the best thing too but it hasn't slowed my hot flashes down. LOL
Hope she finds a bit of relief but this is one thing there is not clear cut remedy to fix, it's just the body readjusting to the change.