Thank you so much for this insight. I was wondering about those little bits of blood inside the feather when I was cleaning the wound! This bird is the oldest one of the flock, so I think it makes sense her adult feathers would come in first, too. My question is... will this start up happening with the rest of the hens in the next few days?! Or is it because this bird is lower in the pecking order that she has been chosen? I also mentioned earlier, but they started pecking the back feathers of another one of the EE’s.
So far thede two injured EE hens don’t seem interested in pecking each other’s feathers/injuries, and the mean girls seem to mostly be the RIR’s. Do you think they’ll be able to get along long term? Or should we consider splitting the flock? Would the addition of a rooster make it better or worse?
Thanks again for all of your help!! There is definitely a bit of a learning curve it seemsWe are so glad to have found BYC!
It's hard to say whether a rooster would make a difference. If you're thinking of adding one, I would wait until everyone is laying eggs so they're ready for the rooster's constant attentions, and be ready for some squabbles as they figure it all out. I would also make sure everyone has healed before considering adding one - because the mechanics of rooster/hen mating interactions involve the rooster standing on the hen's back during 'the act'.
If there's anything I 'hate' about chickens (I have a flock of around 150) ... it's their love of blood. If you have a way to monitor the chickens to see if you have a chief instigator or two in the plucking, you may consider separating the offenders to see if it can stop without the leaders making the first move. I had 2 barred rock hens that would mug other hens - just walk right up and yank feathers out, working together. Didn't even have to be blood feathers. They had their own separate condo/run and after a year and a half or so finally stopped (many supervised visits) and have been with the main flock ever since without issue.
I'm glad the two EEs are looking to be good healing partners. Depending on what your RIRs do or don't do to each other when the blood feathers come in- you may want to consider rehoming one group or the other if things just aren't working out- with full disclosure to the new owners, of course, if the RIRs are chosen for rehoming. That's easier said than done, I know.
In the coming days/weeks, feathers will start out like you saw on your EE hen, so I would look at each one every couple days so you'll known when one is about to be vulnerable to the blood feather vampires.

Sometimes it's something of an invisible process when going from the multiple baby chick molts to their first adult feathers. Hereafter, when your hens molt as adults for the first time, they will (in varying degrees) drop feathers and you'll see them covered in the same look as your EE's back all over their bodies.
It could be that the RIRs won't tolerate what they've been inflicting on the EEs and they might not do it to each other. But you'll find out pretty soon, either way. Ugh.