map,

Thanks for your question.  It's impossible to answer your question adequately with the information provided.  Nightly fever, combined with her fatigue is a major concern and needs to be evaluated by her physician.  She will require a full evaluation including a complete history, physical examination, and then some testing.  Your doctor will decide on a plan of action after his evaluation. 

The spectrum spans from very minor problems to very serious issues.  The possibilities are numerous and include: infection; medication reaction; blood disorders; inflammatory diseases; metabolic disorders; and, even a small possibility of an underlying malignancy.   At this point, it's a guessing game that requires a closer look, and I encourage you to make an appointment with her physician soon.

Best wishes.

Martin Cane, M.D.