Apologies all for the extremely late reply - I've been busy re-vamping my chicken coop. Ok, so the avian specialist saw B yesterday and after taking a look at her poo under a microscope, there's no sign of any parasites. She had an ultrasound and there was no sign of any reproductive activity, so no egg that was stuck. There was food moving from her crop so her digestive system is working. There was a fair bit of poo so it seems as though she was constipated but that's definitely stopped now (the amount of poo I woke up to this morning was insane! Was so happy to see it though) I asked why her tail was still down and he seems to think its to do with the constipation and also stress - Beatrice was hurt a few months ago by my dog. Maggie got out of her crate when the girls were free-ranging and chased B up the yard and 'played' with her. She hurt her leg and every now and then Beatrice limps. He seems to think that the cold weather has affected her leg, which has stressed her out and caused the tummy upset. He advised me to keep her warm so I've been looking for a brooder lamp and I've cleaned the coop and put more hemp in there with them. The chickens are cross bred in the region to help them with the climate here, but I still want to make sure they're nice and warm.
I appreciate everyone help with this. I had no idea what to even look for so I'm incredibly grateful to all of you and your great advice.