Pattience I don't know if this will be helpful to your sister or not, but I've read the Overfed Head and now reading Overcoming Overeating. I wouldn't call it a method or a diet, it's an anti diet and it requires that you let go of the dieting mentality and releasing yourself from the confines of restriction. It sounds really hard to do but it hasn't been difficult at all - it's not without its challenges but it's the type of challenge that doesn't go against your better judgement. Whereas diets restrict you and make you feel bad for eating, IE does the opposite. You're not battling food anymore. You're not saying to yourself that sugar is bad, or bread is bad, or dressing is bad or anything like that. You're staying tuned into your physical hunger and dealing with the emotions that we associate with hunger instead. IE does not make your problems go away, it just makes you stop eating as a way to deal with them.
I've always liked spinach too, and fruit and veggies and even flax seeds. Liking food was never the problem. I wasn't one of those people who never ate a vegetable. And I always loved exercising too.
"If you pay attention to when you are hungry, what your body wants, what you are eating, when you've had enough, you end the obsession because obsession and awareness cannot coexist." - Geneen Roth