They are addicts. They want a quick fix that also does not fuck with their body chemistry.
Water fast is probably the stupidest thing they can do especially when they don't do correctly.
The fasting and ED community have a lot overlap (surprise surprise) and the people who are serious about fasting actually prepare for it. It's not something you just wake up one day and just start doing. Serious folk reduce their calories in the day before, go on a keto diet (remember reading about a guy who only ate sardines in oil for three days prior to fasting), and during the fast make sure to keep their electrolyte levels in check.
I'd love to see Amber try that; seriously I think it could possible be something that might help her.
Let her eat as many sardines as she wants. If that cow can put down more than 2500 calories in sardines then let her; the salt and fat wouldn't be any different than her normal daily slop.
Have her do that for three days (maybe more; I don't know much about the keto diet in regards to death fats) then fast one day. Drink water, coffee, and some electrolytes.
She's feel like shit that's for sure but she'd lose weight.