Well done to spare her lots of suffering!
I am very sorry that you lost your favourite girl. Sometimes there is just nothing we can do to help but put them out of their misery as a last friendly turn. :hugs
I might be vent gleet or not.
When did you last deworm your flock and what exactly did you use for how long?
Worm infestations can cause diarrhea, nutrient and vitamin deficiency, lethargy and neurological symptoms, crop disorders, horribly smelling feces etc.