Hen roosting on another hen??

Some background on these two girls: Both buff cochins, both hatched last March. Elsa is normal in size, nice red comb, started laying in August (very small eggs) hasn't laid since November due to molting. Hazel has yet to lay an egg. She is about 1/2 the size of Elsa, small pinkish comb.
I noticed a few weeks ago that Hazel was missing some feathers on her back, figured she was starting to molt a bit. We have had some bitterly cold temps the last few days and I was checking on the flock the other night and Hazel was on the floor of the coop with Elsa asleep on top of her. These two have never roosted normally. They have been content to sleep on floor next to each other. The next morning Hazel's back was bloody...I am assuming from Elsa's nails digging into her all night. Last night I found the same thing. I picked them both up and put them on a roost. Now I am finding Elsa sitting on her out in the run during the day! Hazel does not look well. I am treating her back with antibiotic ointment, but she seems a bit lethargic. Has anybody else experienced this behavior? Obviously this has been going on for awhile which is why Hazel has had the thinning feathers on her back. I think with the cold temps, Elsa is doing it a lot more. So far the other chickens are not picking at the injuries and I think it will heal up fine if I can keep her from being used as a roost!!

BTW...I don't think this aggression or dominance. Elsa is asleep while she is "roosting". Thoughts??