Tormented older gal

[AEG]

I have a 4 year old gal that is the last from my original flock. My 1 and 2 year olds are all chasing and pecking at her. I had to separate her for the past three weeks to heal a bad wound on her neck. Last night I reintroduced her to the coop when all were asleep. This morning they were attacking her again.
I am getting 3 new 6 month old gals tomorrow. I would like to put them in with my old gal to help her develop some. support. I am using a small summer only coop that is up against the run of my big coop so they can all see one another. First does this make sense?
My big issue is I live in northern Alberta and winters are very cold. I have one coop and need them all in one place using the same run (I do not free range due to predator risk) by mid October.
If I cannot get them to accept my old gal will she need to be euthanized? Other than general aging she has no visible issues. I really could use some suggestions because she is a sweetheart and I would be sad to lose her but I don't want her brutally killed by the others.

 

[aart]

She could have some ailment that is not apparent to humans but the birds know about.
A sick bird is often drummed out of the flock.
Putting the new birds in with her might work, but it's also a risk due to the possibility of bringing in pests or disease with the new birds.