Forcing chickens to be friends

[McChooky]

What I would be looking for is something the other hens have in common that the victim does not; size, colouring, anything that makes her different from the others. With such a mixture it might be hard to see.

EDIT.
ISA brown/sex link I would say is the problem. You've got a high production breed in with a bunch of heritage breeds.

I had a similar problem and separated my heritage breeds from my leghorns

 

[Jenjens]

This article has some ideas that might be helpful:
https://www.backyardchickens.com/articles/chicken-bully-chicken-victim-a-two-sided-issue.73923/

The biggest detail I see in that article, that is not present in your setup, is to put the victim in a place where she is safe but can still see the flock. Not separated in the garage (so she is a stranger when she goes back), but right next to the flock (so she gets used to being there, visible but safe, and eventually is confident in the presence of the other chickens.)

The author of that article is regularly active on this site and quite knowledgeable about chickens, so I would be inclined to trust what the article says about it working in that person's flock. I have not personally tried what that article describes, and of course I can't say for sure whether it will work in your flock or not-- but it might be worth at least considering.

Thank you. I will have to see if I can make a makeshift cage outside or something.

 

[NatJ]

Thank you. I will have to see if I can make a makeshift cage outside or something.

That sounds like a good idea.
I hope it works well