Post 135 has some pictures
https://www.backyardchickens.com/t/68731/laying-hens-with-water-belly-or-ascites/130
You need an18 gauge needle and a large syringe. Do not attempt unless you are 100% sure it's fluids. Even then, know that there is risk and that she could die during or after you try...
I don't want to scare you, but you should know that your hen is very sick and it's probably something that you can't treat. If you have the money, it would be best to have a vet look at her.
-Kathy
Her crop is not her belly. :D her belly (abdominal cavity) is the soft area below her vent. The small pelleted shaped poop could mean that she has an obstruction in her intestines or that there is something, like fluid or a mass pressing on her intestines.
-Kathy
Does her belly feel like it might be full of fluid? Whatever you do, please do not bathe her, she looks way to sick for that. Can you take her to a vet?
-Kathy