I have had to euthanise three birds with EYP. The first time I tried to convince myself she would get better, and I let her hang around for almost 2 weeks in the 'sick bay' before the inevitable had to be faced. The second and third times I made the decision much more quickly. Looking back I regret having waited so long the first time, but I was hoping that I was wrong, and that I would see an improvement, although I now realise that it was never going to happen.
However, every case is different and a lot depends upon the bird itself. The last girl I had to euthanise showed signs of EYP for several months, but just after I spotted it she was full of energy, eating well, pooping a bit weirdly at the beginning but it settled down and even though she was swollen in the rear end and waddled when she walked, she was happy to be bumbling around with the others, so I left her alone. She had several more months of happy chicken life, and it was only when she started to sit down most of the time, lose her appetite and be lethargic I took the decision within 48 hours, whilst the second girl with EYP went downhill rapidly - only a few days between onset of symptoms and the final decision.
However you choose to treat your girl, it will be the right thing for you to do - only you can really appreciate and understand exactly what your bird and yourself are going through, and the decision is ultimately yours to make. We can all offer our opinons and advice, but none of us are there with you and therefore we can't really know exactly what your situation is.
I wish you all the best - know that my thoughts and support are with you, whatever you decide to do for your girl.