I was also diagnosed with CFS some 8 years ago, and have read up a lot on the research. As I am sure you know the medical profession do not really know what CFS is caused by, and to my knowledge no link has ever been proved between over-training and CFS, although of course there are similarities. In my case although training hard at the time, it came on after a touch of flu. It is not uncommon for CFS to be triggered by a virus.
I have thought many times that my level of fitness might have been why I was never as badly affected as the people who become almost bed bound, their fatigue is so severe!
The unrefreshed sleep, and delayed post exercise malaise are of course also classic CFS, as experienced by many people who get CFS, whether they had any sports background or not. So I would caution against thinking of it just as being sports related, and of just training out of it with the help of sports centric advice.
I tried to train my way out of it, and kept crashing. It is very hard to judge if you are doing too much, it only becomes apparent the next day, and in my case in the early days it could be several weeks before I felt OK again.
I eventually came to realise that intensity of exercise was much more likely to push me over the edge than duration, so long slow walking/hiking and then running became my training. Going to a low carb diet helped me enormously.
In my case I have come to the realisation that my days of serious (at my level anyway) alpine climbing are over, but I have got back to a level of health and fitness where I can enjoy long multi-day treks with my wife. We did the Annapurna circuit last year, and are doing the Haute Route in the alps next year.
This is because it feels like it is never going to go away completely. I can still do a bit too much some days, but I am generally over it in a day or so now. I just decided the risks are too great of doing a bit too much on a climb and struggling to be able to find the energy to get back down again. Not fair on my partner either of course.
If she is keen to push herself to race again, then this might not be what she wants to hear, and I hope she gets a fuller recovery than I have managed. But if she can find a way of enjoying being in zone 1/2 then something like recovery is definitely possible.
I wish her the best