I think your vet is conning you, all cats get weighed with their fur
Dont your cats get weighed as part of their annual health check? She should be weighed and a record kept, sounds to me that you need a better vets! They are willing to do tests and keep taking consulting fees from you but not do something so basic as weighing her.
Then they recommend a different Hills diet but dont explain why.
You are the client, you instruct them to weigh her and tell you how much she weighs, and before they do it ask them what is the normal weight for a cat her size.
You say she has an eating disorder but more like she is just a fussy faddy cat who knows she can get what she wants eventually LOL, yes there maybe a problem and I think someone said it may be related to how well she can smell. If she suffers drom asthma this may also not help.
Hills AD is quite smelly and it is very tasty..............ummmmmm so I have been told. My vet in London suggested I try it on crackers, one of his vet friends did
I hate the smell of it and after 4 yrs of finger feeding....................., it also stains and Kocka used to have one paw stained with it cos that was the one she used to wash her face after eating it
I think you need to sit down with your vet and have a serious talk.