bullying hen

Can anyone advise me?
One of my chickens has suddenly - this afternoon, started big-time bullying one of the others.
She's chasing her around, jumping on her back and tugging at the back of her neck. The poor little thing is terrified - she dropped a soft egg on the lawn and pecked it - i think she was realy distressed.
I've put them back into their run as it's nearly bed time, but she still won't leave her alone.
The third hen is the boss of the trio, and she keeps pecking at the bully to tell her to stop.
I can't separate them as we simply don't have any alternative accomodation!
Any ideas would be appreciated  :cry:

Definately a girl - she gave us a whopper of an egg today!
She used to be our favourite but today she's looking like pie material!!

We have that problem with Ginger from time to time and she gets put into isolation for a while.

Their hormones will be running riot in this heat.

Might be worth checking her for lice. Mine had them and one hen used to pull feathers out of the other and eat them.

Talking of chicken sex change we have seven hens two which have not laid since last year and on Sunday morning when I got up to let them out I though that’s a noisy pigeon on the roof sounds like it's been smoking woodbines! but no, the sound of cockerel was coming from our hen house.......OMG :shock:  

It hasn't happened over the last two mornings thank goodness and we can only guess that it's our RIR and hope that nothing more comes of it.