I agree with everything stated here, but maybe not in the context of this particular person. Sounds like she has an eating disorder, with her (excessive) obsession with not getting fat. Obviously getting fat is a bad thing, but I think the fact that she has a real fear of it makes this different. Fear is not required for weight loss/maintenance, just CICO. I get the feeling that, as she's so fixated on this, she probably knows proper nutrition but uses bingeing/purging or restriction as a coping mechanism. This is all speculation of course, though. I don't know her personally