If she gets it as the result of Herxhimer, even on low doses, CDS, other ways of using it, etc. My thought would be that there's something really serious going on - to the point where explosive diarhrea is "the least of her problems." I'm no expert, by any means; but, my own "solution" would be to pick the method which causes the least problems, stock up on depends, stay well hydrated with sports drinks that have electrolites in them, eat a healthy diet, and try to "ride it out" for a few days, to see if it improved. Someone should stay with her during this time, if she decided to go that route; since, it could be dangerous, even with low doses, etc. if her body is THAT toxic. If it's an allergy to the citric acid, using CDS and other methods should help. Although it sounds kind of counter-intuitive, she might try "cleaning out" using it in enemas; since, there might be a heavy build up there and/or some parasites residing there. Also, I've heard of folks putting MMS (I can't remember if it was activated or not) in a humidifier. (I'm thinking that this is mentioned in JH's book; but, I'll leave it to those who've been through training to give the details about this.)
I'm really not liking my suggestion of what I'd do if it were the result of Herx'ing; and, almost deleted that part; but, the fact does remain that IF her body's THAT toxic, something really serious is going on. She could be absolutely loaded with heavy metals, other pathogens, etc. A very slow remediation would be preferable; but, that (FOR ME) would be a last resort effort. It's DEFINITELY NOT something I'd do without having ruled out a sensitivity to citric acid, trying a slower detox (perhaps adding part of a tsp. of CDS into a bottle of water and just sipping on it throughout the day), etc.
Here's hoping that it's just that she's sensitive to the citric acid; and, hopefully, someone who knows a lot more about this stuff that I do can give a better "last resort" option than this.