Excellent suggestion!She sure looks like a character to be reckoned with. Does she get along with that canine dude? What a pair!
I have been thinking about her all afternoon, and after you described some of her food preferences, I'm beginning to wonder if she has a condition called pendulous crop, especially after seeing photos of her in profile.
This is a condition where the crop isn't supported adequately by the chest muscles, and that causes it not to properly empty each night. In fact, it may not empty completely by morning, and this could cause her to feel "full" and not have an appetite.
Years ago, when I had only had chickens for just a few years, I had an EE who was getting skinnier and skinnier. This was in spite of her always seeming to have a full crop. In fact, it was often so full, it swung down low like heavy baggage.
I was clueless. That precious hen had pendulous crop and I had never even heard of it. She finally got so weak, she could barely walk. I had to euthanize her. If I had only known that I could make her a crop bra to support her heavy crop, it would have emptied as it should, and she could have led a normal life.
I realize your vet has ruled out crop issues, but please do a crop check tonight, and again in the morning before you offer her anything to eat. If her crop is still full, then we will know that this quite possibly could be the reason why she's losing weight. Her food simply isn't being digested and she isn't absorbing the amount of nutrients she needs to maintain weight.