Chronic illness since surgery a year ago

To whom it may concren:

My manager became severely ill a year ago at a holiday party, she was rushed to the emergency room and later had to have gall bladder surgery.  Since that time, she has missed a lot of work due to illnesses that vary from flu like symptoms to bladder infections.  She was extremely healthy prior to this and she is in her early 50s with a healthy lifestyle.  She is not overweight and has no bad habits.  She is becoming depressed over the fact that she can't seem to get herself well and none of the treatments so far have solved her problem.

She was told that her immunity system was down (stress) and so she was susceptible to everything – she was told to take vitamins.  They made the throw up.  She has had blood work and tests and still each “guess” seems to be wrong.  She will feel better but never well and it is starting to wear her down.

I feel this is tied to her surgery but I am not quite sure what it could be.  She had a hysterectomy many years ago but now after flu-like illness, she has had trouble urinating and now it is painful – burning.  

She is at her wit’s end and doesn’t know where to turn – she is active and just wants to feel well again.  She has never been 100% since her illness and resulting gall bladder surgery.  

What could it be?