The vet called just a few minutes ago and said that Biscuit's lower abdomen was full of cancerous tumors. Those caused a blockage in the intestines which slowed everything up...causing the sour crop. He said that it looked like it had been going on for quite awhile because she was way too thin. He said we probably just didn't notice her decline which is true. He let us know that we did the right thing which made me feel a lot better. I had a dream, last night, that he told us that "we put a healthy bird down" and after that I never could go back to sleep. I feel so much better now and at peace with my decision. Luckily, I now know where to take my chickens if we need a vet. He loves chickens and wants to learn everything he can about them.

Even though it's sad, it's good that you were able to have a necropsy to find out more information and know there was nothing more that you could have done and this gave you some closure. You are lucky you found a caring vet that is wanting to learn.
A lot of us do our own informal necropsies, it is a learning experience each time.