C.G.
My son recently had a high fever for 10 days... and we went to the doctor throughout the week... where they eventually did a blood test (to rule out bacterial infection) and a chest x-ray (to see if the virus had settled in his lungs)... and they finally found it in his lungs and saw that he had a viral pneumonia!... which has now been resolved with antibiotics. We're all finally getting rest again.
You should definitely insist on further testing or get a new doctor... although a cold and/or cough can last up to a few weeks, I was told that a fever should not last more than just a few days!...
Good luck... I hope she feels better soon!