Sour Crop?- Lethargic chicken drinking an excess amount of water

[StarLover21]

This morning I found one dead chicken in my coop. She had no apparent signs of trauma, and she seemed fine yesterday, so I'm not sure what happened.
Now, I have a rather lethargic chicken. She has simply been sitting next to our duck pond, and drinking an excess amount of water. She seems fine upon examination, except that she smells off. I brought her inside with some food and water, and I'm not sure what I should do next. She is a very special chicken and I really don't want her to die. Any ideas?

 

[StarLover21]

I definitely think it's sour crop or some problem with her crop. Her crop is very enlarged and squishy- it feels kind of like a water balloon. I've tried massaging her crop and she vomited up quite a bit of icky liquid. Is there anything else I can do? Should I take her to a vet, would they be able to help?