Is everybody an idiot? I fast 7 days every spring and have done so for 20 years. The only thing it will do is make her feel better and might cure her diabeties. In addition I fast each monday which off sets the weekend binges. It takes 90% of your total energy just to digest what people stuff in their mouth. You would be suprised how good you feel when all this energy goes to repairing your body. If she was writhing around delusional in a lawn chair there was something else wrong. I suggest she be checked for iligallities or liberallities.
I can tell you have actually done this. A couple of times a year I fast for a while too. I don't have any set time, just however I feel. But it usually lasts a couple of weeks. Its interesting how much the craving for food is psychological. It is good to tell your body "no" once in a while.