Chronic Fatigue Syndrome is very complex. It is often difficult, but most helpful, to figure out what has triggered the CFS. Sometimes Lyme, sometimes a stealth virus -- and there are other causes as well.
I highly recommend the book, From Fatigued to Fantastic, by Jacob Teitelbaum, MD. This book has over 400 pg. of thoughtful commentary on medical, alternative, and self-help measures for those w/CFS and/or fibromyalgia. The author is himself a sufferer, and has oriented his clinical practice to research on effective treatment for these conditions. I found my first copy of this book at the public library, but it was so helpful I ended up purchasing the most recent edition.
I suggest that you tell her to get adrenal and pituitary glands checked out. Maybe the thyroid as well. Also, has she gotten her hormone levels checked? From what I understand, when these different glands in the body aren't working correctly, they can cause a number of problems, such as fatigue. Maybe suggest she see a naturapath. If they are out of balance, a naturapath may give homeopathic supplements to help get her energy back. A naturapath may also suggest diet changes so that these types of problems don't happen anymore. Hope this helps!
I agree with raylp. A very high percentage of those diagnosed with CFIDS are later, with proper testing, found to have Lyme Disease. CFIDS, then, is felt to be a symptomology of Lyme, as are many other illnesses these days - Lupus, MS, ALS ... and the list goes on. You could do research on Lyme to find out how widespread this disease is becoming.