Niacin can cause flashing. But so can other medical conditions. I would contact her doctor for guidance. A quick google search indicates that it is not uncommon for women into their 80s to still experience unexplained hot flashes.
peaches, have Mom's primary doctor see if he can solve the mystery.
One thing you can do, if possible, see if you can keep a log of what food she eats, when she takes her meds, what she has for snacks, etc. and see if there is a pattern of when this happens. Maybe this happens right after she has coffee or soup, which will heat up the body.
One thing you can do, if possible, see if you can keep a log of what food she eats, when she takes her meds, what she has for snacks, etc. and see if there is a pattern of when this happens. Maybe this happens right after she has coffee or soup, which will heat up the body.