Hi Melissa,
When my RIR pullet started laying, her normally sweet personality changed and she began pecking and eating the feathers from our red sex lin's lower back. Over the course of several days the behavior increased so that she drew blood. We removed her to a temporary cage inside for a while (I can't remember now, 4 days or so?) in hopes that by re-introducing her she'd change. Apparently that HAS worked for some folks. Unfortunately not for us. I also tried BlueKote and mentholatum on the victim's back, but the aggressor just switched to haunches instead, and started attacking everyone of the other 4 girls, even when she was happy/busy out free ranging!
It became obvious we couldn't keep her, since we have such a small flock and she was disturbing the peace so badly. Angie n Maine, a member here, adopted her. Angie has roosters and her birds free range all day. Apparently our girl (Hazel) is doing very well there, no bad behavior at all!!!
Maybe you could try a "vacation" for her with another flock (though then you have the whole quarantine issue) to break her of the habit?
Good luck, you have my sympathy!
Stacey