Sorry about your problem. I have hypothyroidism and have the very same problems. I can not tell you anyway I have found to stop this, but I do know that it has effected my time out in the public. So I would like to know too.
Hyperthyroid can cause this. Not sure you age or situation but being premenopausal can also casue seats. The symptoms are similar with both. I have and had both and it is very fustrating. WIth premenopause the same things start hot sweats for me. If I can I try to sit down , have some cool water and wait a bit before moving around. If she thinks she has a thyroid problem you should be tested. I gyn can do test to see if you are perimenopausal. There are some natural things that are suppose to help with this.
I'm hot all the time too - but T3 T4 TSH are all in 'normal range.' I'm pretty discouraged about it.
Interesting, I tend to be cold and think I am hypo though my bloodwork is normal. My thyroid is enlarged though and I am waiting for more tests. I do however sweat very easily and embarassingly profusely too. Its like I have a very small comfort zone temperature-wise.