My mother has all these weird health-crazes that she follows... and they change weekly!!?

You have to face the fact your mother is not the smartest person in the world. She is easily influenced and not very bright. If you can get her to a Dr that might help, she should be drinking water or she will endanger her health (as you have stated). Go with her to the Dr and tell him whats going on and make sure he explains the dangers of these health fads to her.