My dog is always refusing food and I dont know what to do

Im trying to post here because AskVets hardly allows anyone to comment and I need help.

Required info: Female, Dog, 12YO, Yorkiepoo. About 9lbs. She has a history of bile reflux which she was treated for about 5 years ago. Also has a history of HGE once, possibly twice. I have no access to any test results from the past.

My dog has always had problems with food/eating. She had bile reflux for years before they figured out that that was what was wrong with her and treated her with medication and afterwards she was like a new dog. Now within the past year or so shes consistently (maybe once a week/biweekly at most) refusing to eat sometimes again.

Just about 2 months ago I had to take her into the ER vet at 3am because she had refused food that day and started diarrheaing blood. No stool just bright red blood. We were there for 5 hours and they couldn't figure out what was wrong with her. They did blood tests, an ultrasound and an x-ray. They said everything was fine besides her platelet count being high (I believe it was platelets i could be wrong, it might have been white blood cells, i dont remember). She stayed over night for fluids and nausea medication and I picked her up not even 24 hours later because she was 100% better.

They tested her for all tick and flea borne illnesses even added another $300 to the bill to send a test out to cover all bases. All were negative.

That cost me $3200. I put it on my Care Credit because I cant afford anything like that. Im beyond myself as shes been having diarrhea for 24 hours and is now vomiting twice an hour or so (just bile). I dont know what to do for her. I cant afford to keep adding vet bills. They can't tell me what's wrong with her and they say she doesn't need a special diet. Ive tried pretty much every food/combo of food I could over her 12 years. Nothing seems to work for her.

Shes got an appointment for 11am tomorrow because I cant let her suffer obviously. I just have to accept whatever they want to charge me and go into more debt. Is there ANYTHING I should be asking about? Anything she needs to be tested for that they haven't done yet? Do I need to insist on some special diet that i cant afford either? Im at my wits end, but she is my baby.