Cafarm girl is right - it affects different hens in different ways.
I have a hen - Little Miss Shy - that had EYP - she got very swollen, passed ribbons of 'cooked' egg, and looked very sick. I checked her out but couldn't find anything stuck or broken inside her, so I gave her antibiotics for a week (amoxycilin). She eventually perked up, and is still with us 5 months on. She runs around with the rest of the flock, eats well, and fights for treats, but is swollen in the rear end, walks like a sumo wrestler, and drinks huge amounts of water in order to liquify her droppings enough in order to pass them easily. She has stopped sitting on the nest and not laying, so I assume that her system has stopped producing eggs.
Her sister (Braveheart) started to show signs of EYP two months ago, - she was sitting on the nest but not laying, and this went on for a long while. The all of a sudden she went downhill rapidly, and very sadly I had to euthanise her after 10 days, despite trying everything I could to save her. However Little Miss Shy is still going strong. It seems to affect each hen differently, and we just have to react to each case as the symptoms dictate.
I have lost two hens in a very short space of time to EYP, and it is the most horrible thing to have to go through, but at the end of the day you have to decide if the hen's quality of life is being affected. So far Little Miss Shy shows no signs of being in pain or distress, and joins in with everything the flock does, so I will let her live her life, even though waddles when she walks and she has a rear end wider than mine (and that's saying something!) As soon as I see that she is starting to suffer I won't hesitate to do what is necessary. I let her sister suffer for 10 days, when I should have put her out of her misery sooner, but I was hoping against all the odds that she would come through it, as Little Miss Shy has.
It is normal to feel bad when you have to take the life of any creature, especially one that has been a pet or companion, but in some cases it is the only thing that you can do to help them.
It is true that you can get implants to help a chicken that is not too far gone with EYP, but it depends upon having a specialist vet nearby, and also having the money to pay for the procedure. We do not all have the facilities nor the means to do exactly what we would like in life - if we can then it is wonderful for both ourselves and our pets, but if we can't then we just have to make the best of the situation that we are presented with.
I hope that your girl can continue to carry on for a bit longer - if you can take her to a specialist vet then you can get some professional advice to give you a clearer idea of her prognosis. But in any case, I wish you the best for both her and yourself. Only the person who is present and who knows the chicken can really know what is best for their flock at any given moment. Whatever your decision, whenever you take it, you know that it will be the right decision for you and your girl, and that you will have the support of all the BYC members.