One of them had a quote from her and a picture from when she was a teenager and looked of a healthy weight/a bit chubby and she said at that time she had an eating disorder and that she wasn't healthy, regardless of her appropriate size.
This is something women in the fat acceptance community say all the time. It is almost never true in the sense you're thinking. They have an eating disorder: it's binge eating disorder (BED) and emotional eating. What they claim is that they were anorexic, and that when they were less fat it was due to anorexia (sometimes, bulimia), and that there's absolutely no way for them to become thin, because they were "anorexic" and "still fat" and insist it proves that some people are just fat even if they eat nothing, and you wouldn't ask them to be anorexic just to get down to obese, would you?
What happens is they feel bad about their weight, and eat less for a day or two, then binge again (a lot of them descend upon the MyProAna forums to talk about how ana they are, because they never could possibly have BED or emotional eating oh no, it's ana all the way.) Sometimes this is enough to halt their gain for a while, and it certainly isn't a healthy pattern, and very stressful, unsustainable behavior. They consider this to be either dieting or an eating disorder, depending on the day.
Then, when they decide to "recover" from this eating disorder, they dive right into a nonstop lifetime binge. And if you ever suggest portion control to them, you are triggering them back to their eating disorder.
It
sucks for actual sufferers that these whales had to go and co-opt eating disorders and their attending issues: triggers, health at every size, intuitive eating, mindful eating, etc. They took every good tool from ED recovery and twisted each one into an excuse to binge, and to justify never being questioned about their weight, eating habits or nutrition, lest you "trigger their ED".
What I'm saying is: Whitney doesn't deserve your sympathy. Eating disorders suck, but they require an abundance of something Whitney has never possessed: control.