VERY poorly hen, help

Ok so the hen who came home from the farm with the blackening comb has deteriorated, not been helped by the original 5 hens bullying tactics. 

Her symptoms are; stopped laying (before she arrived), blackening comb, severe lethargy (started today) not eating, drinking, fluffed up, laying down (but perching now I've put her up) bare bottom (some green spikes, feathers? sticking out) and watery poo.

Will post a pic tomorrow but any suggestions would be very appreciated

Yes Joy your right, need to find one first as ours isn't keen; cheek.  I've also just had a talk with Andrew (who she came from) and he didn't hold out much hope when she came to me.  Eils made some porridge tonight and hand fed her a few spoonfuls, she's perched with the bantams just now so we'll see how she is in the morning.