I'm so sorry to hear about Joey, I hope she gets better soon. I might be able to give you some hope, my fiance and I went through a very similar situation with Priss several months ago and the result was positive!

I gave Priss a piece of Chick fil a chicken from my sandwich I had for dinner on a Wednesday. We're pretty sure this is what caused her sickness, and my massive guilt I just love to spoil them. Wednesday night she threw up all over the apartment. We cleaned it up and hoped it was all out. Thursday she stopped eating and continued to throw up, just not as much since she wasn't eating. Friday she still wasn't eating, wasn't going potty and was very lethargic, we got her to the vet as soon as we could on Saturday morning. We had to leave her there and wait until they could make time for her. The wonderful vet stayed late to take care of Priss, she examined her and did an x-ray, she couldn't see anything wrong. She told us to take her home and force feed her with a syringe and gave us anti-nausea medicine to give her, it was horrible, we felt so bad having to force her to eat all of these things (but I was glad we didn't have to give her any pills, it was all liquid), PLUS keep her in the bathroom so we could monitor if she was eating and using the litter box. I made her a very cozy nest during her stay in the bathroom, she is after all, our princess. We took naps and sat in there with her and my fiance even slept in there with her part of the night (they have a special bond and he was so concerned). She slowly but surely started to get more energy and started to eat again because of the anti-nausea drugs (she wasn't eating because she knew she would throw up). Finally she was eating her special food by herself rather than us having to force feed her and she was using the litter box. It was a slow process but we finally got our Priss back. All of our cats get very minimal table food now, they have only gotten fresh chicken and turkey since and that is at minimal quantities. My fiance is a stickler about it now since he was so shaken by Priss's illness. We are all happy and healthy now though!

My guess is that Joey ate something that disagreed with her and is probably not eating because she was throwing up, much like my Priss. Don't worry, she'll be fine. Have patience and she'll be home soon and you can nurse her back to health. I hope my story helps you feel better! Good luck!