I have many friends who have tried various detox diets and they all do the same thing from what I can tell: they totally flush out your system in such a way that you might as well have a telephone installed in the bathroom because you won't be anywhere else!

A lot of water weight is lost, you may feel sick

and then your system evens out. After awhile, you can start to eat normally again and you gain back all the weight that you lost.
I had a friend who did the cayenne pepper detox diet and it sounded absolutely horrific that someone would put themselves through such a process! She and her roommate were so sick from it that, in my opinion, the benefits did not outweigh the misery! You may want to take a look at this article on detox diets:
http://www.msnbc.msn.com/id/18595886/I have found that if I get the urge to detox (which isn't very often, mind you) then I just take a day and eat mostly fruits and vegetables and drink lots of water. That usually does the trick and I don't have to intentionally punish myself. I'd also suggest that she have her blood work done and see if she is low in iron or if there are any other unseen things going on.
So there's my 2 cents worth. Hope it helps.
-Lisa Marie