Low grade fever and chills can be a symptoms of Lupus or other rheumatological issues. Your mother might consider seeing a rheumatologist.?
I get chills and body aches, nerve and muscle pain. Kind of like having the flu but not exactly. The chills come on fast and can be intense for about an hour or more- I also go to bed to try to get warm. I continue to be somewhat chilled for 24 hours or so. I am generally cold intolerant in the winter, meaning if I get cold its hard to recover- hard to warm up again. I have some arthritis also that is related.
It was my hematologist's idea that I see a rheumatologist. After much searching I found a rheumatologist (nurse) that I like. Through extensive blood testing she diagnosed me with Lupus and Sjogrens syndrome. Lupus and ITP often go together, not sure why but some people who have ITP develop Lupus. And people who have Lupus can develop low platelets. I now know that when I have chills it is a Lupus flare, so I can take prednisone to calm down the immune system. I also take Plaquinil which helps prevent flares. Also I try to do other things to take care of myself and avoid my known triggers- dress warm, reduce stress and no more working long hours. Good luck finding your answers!
ps. I also get a malar or "butterfly" rash when I get chilled. Its a blushy redness across the nose and cheeks.