mean chickens on strike

[angry chicken]

I have Americana chickens. for some reason they all picked on one hen and almost killed her she was a bloody mess. I took her out and apart from the rest. She is well and pretty got all her feathers back. But every time I put her in with the rest of the chickens they do the same. I've tried a few times but have given up. Also my hens have stopped laying. They are 3years old. They haven't layed for months. I know if its too hot or if there molting they wont lay but its November. What now its too cold? I live in Texas the weather has been around 60-70. But still no eggs.