Hello and Welcome to the forum, Vijay!!
I'm sorry to hear that your mum suffers from RSD!!
I have RSD in my left leg and both arms and it is an awful condition! I developed it when I was 12 years old after an ankle sprain and am now 14.
I also get the hot irritating sensation that you mentioned and it is extremely annoying sometimes!!! Sometimes it tends to hurt a lot whilst other times, it is itchy and as though I can't sit still for short periods of times and am always fidgiting. I read somewhere that it can be a common symptom of RSD.
I haven't found anything that helps with the hot sensation so far, sorry.
What sort of doctor does your mum see??? It is extremely important that she goes to see either a Pain Management Doctor or Neurologist as they are usually the best doctors to treat RSD.
Does your mum have any Physical Therapy? It's really important that she keeps moving - even though it hurts a LOT!! RSD is a 'use it or lose it' condition. Your mum could do some gentle exercises at home should she wish but it's always best to see a trained PT who specialises in dealing with RSD and other similar disorders.
Unfortunately, there is currently no cure for RSD. The condition CAN be managed though by the use of medications, PT, nerve bocks, pain pumps etc etc.
Take care and please send my love to your mum.