Hi, welcome to BYC!
You did the right thing by isolating the bully hen. Let her live alone for a week or so, then reintroduce her. In the meantime the other hens will re-establish their pecking order, and it will not include her. Then when she comes back, she'll be at the bottom of the pecking order until she moves up again, and that might settle her down.
If she pecks again, I would put some pinless peepers on her. You can buy them from almost any poultry supply place, and some people have had luck buying small quantities on
eBay. They are like plastic blinders that fit into the nostrils and stop the hen from seeing the end of her nose. She can still eat, etc, but will not be able to see well enough to peck. I've used these with great success before. Once she's worn the peepers for a few weeks, you can take them off and see if she's reformed. If not, you can put the peepers back on. Or eat her (which is what I would do, since I would feel like I'd really given her a chance to reform!).
You might want to buy some Blu-Kote if you haven't already. It works well for pecked-hen injuries because it not only is an antiseptic, but it covers up the red wound with a dark blue color. Since chickens naturally peck at red, the Blu-Kote helps to keep other flock members from worrying the wound. You can buy it at
TSC or any other ag-supply store.
One thing to watch out for: you said that you turned off the artificial lights. If you were using lights to get light-hours up over 14 to stimulate winter laying, turning off the lights for even one day may throw your flock into a moult and/or stop them from laying.
