Chick pulling out her OWN feathers even with anti-pick lotion!!!

So I have this 4 week old polish chick who was totally fine when I left for work this morning and her whole back was bald when I got home. She has been housed since day old chicks with 5 others (all day old 3 silkies and 2 other polish) and there has been no picking. They are all on pine shavings, eating Purina Start and Grow (medicated), have free choice grit, and each get a few dried meal worms per day as a treat.

So I figured she was getting picked on and seperated her and applied pick no more lotion. BUT....she is the one pulling her own feather out! I know the pick no more tastes bad as she freaks out after picking but I can't get her to stop. Has anyone had this ploblem? What should I do? She is my favorite (of course!) and I just want her to stop!

Thanks in advance!