Black tips on comb and runny poop

[Arla]

I have a 3 1/2yrs old Warren hen. She hasn't been herself recently. She has been lethargic and withdrawn for a few days. She eats very sparsely and doesn't drink alot. Her crop is quite baggy. I can feel some food and fluids in there. No noticeable smell. Her poop has been runny and started making a bit of a mess on her feathers. And her comb is looking a bit weird. It has black tips and has a purple blotch on it. I'm not sure if it's frostbite. It has been cold a couple of weeks back but not recently. She hasn't had any problems with the other hens but I have taken her out onto my lawn where there is grass and she is quite happy but very slowly walking around having a scratch and the odd peck. She didn’t seem overly bothered about chopped egg?
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Any help/ideas/suggestions much appreciated.

The black tips on her come are frostbite. I don't know if the frostbite is connected to the other problems. Hope it all gets better.