It won't hurt to add protein to the ration and see if it improves the situation, but feather picking can be much more complicated, especially if it becomes habit.
I recommend you also set up time to observe your little flock to see what dynamics are in play and identify the culprit(s).
There are a couple of approaches you can try, once you identify the perpetrators, but it may be just one causing the problem. First of all, you need to protect the victim. I've had good results covering the victim with a saddle apron so the feathers can regrow. Or you can separate the victim by giving her her own compartment in the run where she can be safe yet still commune with the others.
Another approach is to install pinless peepers on the main picker. This helps by restricting her vision so she can still see to eat and drink but she can't see straight ahead to focus on her target.
Be warned, though, if the picking has gone on for a while and become a habit, it can be very hard to break, chickens being especially fond of habits as they usually are. And the act of feather picking can be passed on to others, also. It's can be a very difficult problem to deal with. I wish I could tell you there is a sure-fire cure for it, but I had a gonzo thread titled just that
https://www.backyardchickens.com/t/697052/i-think-i-found-a-miracle-cure-for-feather-picking, and it turned out there is no cure and no lasting solution for it.