Bared bottom hen

Here I am again with another piece to the puzzling condition of my 5 1/2 old big buff rock hen. (I posted last week but can't find the post) so to summarize:

The beginning:

blood on the poop board (no poop, some tissue)
squishy, bloated belly
falling, off balance
yet eating and drinking

INITIAL TREATMENT:

brought inside home for 2 days
warm bath
yogurt
apple cider vinegar in water


RESULT:
finally laid an egg (2nd ever)
walking okay
put back into coop

END OF NEXT DAY:

Her bottom around her vent is plucked clean. It is not red, but still squishy. (I don't know if the squishy big bottom is typical of a large hen)

I've read a lot of threads concerning bare bottoms, but found no answers though it happens a lot.

It's getting cold now, wondering if she needs extra protection and if there is something anyone can tell me the about her plucked behind and what to do about it.

Thanks!

 

Thanks Judy for the direction. I was able to find a previous post before but it's been a while and have since lost my way. This time around I only gave it about 5 minutes - which is actually quite a long time these days Any help/guidance for my hens dilemma?