Hen mating another hen

It just sounds like a dominance issue to me. But someone else may have a better opinion for you.

How old are these hens?  And do you happen to have a picture of the dominant one ?

It is a pretty common occurence particularily when you have no rooster.  Quite often one hen will assume the dominant role even to the point of crowing.

Would they start to grow spurs too?  I got some leghorns that were without a roo and one of the hens has spurs.

I am not sure there is a species that there is not some same sex mating activity displayed.  On the farm I have seen male on male and female to female action displyed in Horses, cattle, pigs, dogs, cats, ducks, geese, goats, sheep.  Look at a pen of cattle on feed and the riding of each other is a nuisance and in some cases drugs are fed to minimize.  Bulls will ride a less dominate bull to its death.

Castrated animals do it also.  It is an acitvity as common as the animals themselves, hardly worth note in my opinion.

It is a dominance issue.

Just a quick thought from me.  I sometimes get hung up on semantics and gets me in trouble.  I would not describe it as an issue.  I would describe it as a behavior. 

Dominance issue seems to define it as something that needs to be addressed fixed or otherwise dealt with. 

Dominance behavior is just what they do. 

Behavior in animals and pets that affects our ability to relate to them or other wise enjoy them may be addressed for our safety and or comfort.  Other wise normal animal behavior is best left as is.

Example:  Country kids see a horse poop and take no note.  Kids that have no experience with farm animals see a horse poop or urinate and they ooh ahh and have a fit that a horse would have the bad manners to poop publicly. 

This is not a behavior we would likely modify LOL.