I have three hens that are all 2 years old.   This is the first year that one of my girls got sour crop. ( only alittle experience)  It is terribly confusing to diagnose and treat an animal by myself, but there was no way hubby was going to let me bring a hen to the vet.
 
 I brought her away from the other hens too so I could monitor poo and food and water ( cold wi winter-I took her to stay in my bathtub)  I read so many things to help that I just decided to do it all.  I decided I wasn't going to vomit her though.
 
 Each day 3 or 4 times a day morning and evening I massaged her crop downward and around in circles, pretty firmly.  I'd hear it gurgle, and she would actually burp and feel better.  I knew this because after I did it she would try to eat and move around after just laying there.  I watered down her pellets or crumbles so it was soft.  I think a few days I put acv in the water, but she didn't drink as much with it in is, so I switched to putting baking soda in it. ( to tell you the truth I am not sure what this did)  I also thought I read that oil was good, so I did lightly water down some bread without the crust and put a layer of olive oil on it.  She loved it and for a time that half piece of bread was all she ate in the day.  She's always hated yougurt.  I also sprinkeled some kids culturelle on her wet food.  It took about a week to a week and a half and the swollen mushy crop was gone, and she was acting like herself...but was really tiny!  She seems to be healthy now and gained her weight back rather quickly!  I would say go with your gut with all the different types of treatments, and try the massaging, make sure she has a lot of fresh clean water.