Poor girl.
Treat her wounds as instructed by @Eggcessive
- great advice as always.
If she came with the 4 you bought, instead of completely isolating her away from the others, if you can set up a kennel in the run or section a portion of the run that would be best. This way she is "separated" so the others can't peck at her, but she is still somewhat viewed as part of the flock. Isolating her completely will give you more problems when you try to reintegrate her back with the others. At night, depending on the size of your coop, you can place her in a small pet carrier or wait until dark and place her inside for a couple of weeks, then you will need to "separate" her during the day so she heals. Sleeping with or near the others will reinforce the idea that she is part of the flock, so hopefully you have no drama to deal with.
Just my thoughts