My Wife Had A Liver Transplant 6 Years Ago And

My wife had a liver transplant 6 years ago and has been doing quite well. THis morning she woke u shivering saying she was ice cold. Her body doesn't feel warm or cold and her temperature is 97.8 (normal for her). I am wondering if this could be a sign of liver rejection or a reaction to the tacrolimus (which has been stable for 5 years)???