My fussy dog won’t eat, at a loose end

My 4 year old Shih Tzu has always been a very fussy eater. I’ve had countless trips to the vet since she was a puppy to work out if it’s a medical condition or teeth issue. It’s not- she’s just very fussy.

I finally found a food that she would eat when I mixed it with cooked chicken, Wrainwrights kibble with chicken.

Fast forward, she started getting chronic ear issues and skin issues. Guided by my vet, I did a painstaking 6 month elimination diet, and she is allergic to chicken.

I tried to find a new food, and found all the advice on this thread I should go for the top WSVA aligned foods. I bought the Hills Science Plan (Beef), and she wouldn’t touch it. I tried to make her eat it, and she ended up going 2 weeks without eating a full meal and lost a ton of weight. This is the only WSVA aligned food without chicken.

I know if I were to give her a crappy supermarket brand without chicken she would gobble it up, or eat it up if I coated it with butter or loads of cheese (but this is obviously bad for her). She doesn’t really love any other meats, so adding them cooked won’t help.

Ive tried food toppers, the ‘put it away if she doesn’t eat it’ method, but the fact is she just won’t eat. My vet doesn’t seem too bothered and says she will eat the hills food when she’s hungry, but I don’t agree. If I continue with it I think she will get serious health issues.

I’m stressed out my mind about this and don’t know what to do. Any advice would be welcome. We’re based in the UK.