Well I didn't want to say it, but I suspected she was dying. My guess was her digestive system had shut down, which is why she had sour crop. And the reason I suspected that was the other symptoms.
You can do a necropsy if you want but the most likely result will be that she had a tumor or...
I figure all the real experts are sleeping, and so I will try and give you some things I've learned in the mean time.
1) If you can, take the sick bird inside, perhaps in a dog crate. That way she won't be cold (stressing her more), and you can examine and observe her better.
2) Examine the...