purple comb, legs spread, tail drooping...help!

We currently have 3 ladies in our backyard crew, 2 colombian rock x's and 1 EE. The Rock ladies are about 2.5 yrs old and our EE is just over 1.
Sophia my feisty little rock lady has been sick for about 2.5-3 wks with what seems to start resolving and then comes back, the other ladies are perfectly fine and laying daily.

It started with what we thought was vent gleet. She had runny diarrhea and a messy back end. We cleaned her up, trimmed some feathers and used blu-kote to ensure the other 2 didn't peck at her red back end. I started adding ACV to the water daily and started feeding a yogurt & probiotic mix daily. After a few days she started having semi regular stools and was acting fine during the entire ordeal. She never stopped eating or drinking.
The EE Shirley did briefly for about 1 day have some runny poop but it was also very hot out (35C with humidity) and it resolved as quickly as it appeared.

Now the last 2 days Sophia has gone from seemingly fine to a purple comb, drooping tail, wide stance, head shaking, not eating, drinking a lot and refusing to roost/hiding in the coop/behind things in the run/paddock area. We changed out all the bedding a week ago, its very well ventilated and dry. all shaded etc. She has liquid poop again, when she goes and she looks downright awful. Im at a loss...Ive never dewormed our girls as this has never happened in the 2.5 yrs we've had egg layers. The closest vet that sees chickens is an hour away. Does anyone have any insight?

Sophia could be suffering from egg yolk peritonitis. They can have vague symptoms of runny droppings, loss of weight in the breast area, problems with walking prefering to sit, not lay regularly or have egg quality issues, and labored breathing. There isn't much treatment that can help if it is that. Make sure that she is not dehydrated by adding some electrolytes to her water, and push her to drink. If a vet is available you could get a diagnosis.

Thank you, we made the hard call to cull her as she was suffering. Upon necropsy her abdomen was in fact full of what looked like curdled custard and free fluid. I believe your guess was the correct one.

I am sorry for your loss. Unfortunately, this is a very common problem in hens.

Sorry for your loss.