This is sad... I'm sorry. This sounds a lot like my bird that had Marek's. I'm not saying that's what it is, but, it might be worth your while to research about it. If she passes, and I hope she does not, consider getting her tested... There are links in the FAQ in my signature on how to do this.
Take heart; some birds that go through this DO improve and live quite a while. But... some do not.
A vet will humanely euthanize, for a fee. You can do it at home, if you have the stomach... there are a great number of threads about the most humane way to do this here on the forum if you search. If she were mine, I'd give her more time to see how she does, but the choice is yours and you should do what you think is best.