Here's what I would recommend doing-
1. Try Pick-No-More Lotion (
http://www.mypetchicken.com/catalog/Chicken-Health/Pick-No-More-Lotion-4-oz-p389.aspx)
2. If that doesn't work, I would try Hot Pick Anti-Picking Spray (
http://www.mypetchicken.com/catalog/Chicken-Health/Hot-Pick-Anti-Picking-Spray-4-oz-p1001.aspx)
3. If that still doesn't work, she's probably doing it out of stress, so I would try to fix that problem. Here are some things that could be causing stress, and here are some ways to fix them-
Not enough space- give them more space
Not enough feed and water containers to go around- put out more
Not enough nesting boxes- add another
Worms, parasites, lice, etc.- treat medically
Not enough protein in their diet can sometimes make them behave like that- add more protein to diet
If you try all of these things, and she still behaves like this, talk to me again, and I'll help you from there.
Good luck!
-Ameraucanas