Grumpy old girl...

[chickens really]

Keep her but make her her own spot in the Coop for the times your not around.....

 

[chickens really]

Also putting human emotions on them does not work....She is Happy in her own skin....

 

[rosemarythyme]

If you're fine with having 2 separate set ups, then I think it should just stay that way, with alternating free time. Some animals just don't want companions or don't take to new ones. It might be enough for your single older hen to be able to see other chickens, but not spend time with them.