This type of feather eating is caused by several possible things, such as too little protein in the diet, overcrowding, boredom from not getting out to free range, bullies, too much light in the coop, and others. If you can identify the bully, you can get some pinless peepers to put on her so that she cannot see her victim.
What are you feeding them? Feeding a good balanced all flock or layer feed as 90% of their food is best. All flock or flock raiser is best at 20% protein. Layer has 16% and is the minimum. Most hens need a minimum of 4 square feet of room inside the coop, but they need much more than that in the run, or to get out and roam and peck at grass and bugs.
The bald chicken might need a hen saddle for awhile until her feathers grow back. Some may not regrow feathers until the first big molt, around 18 months old. Here is some reading:
https://www.backyardchickens.com/threads/pinless-peepers-work.480929/
https://poultry.extension.org/artic...ibalism-in-small-and-backyard-poultry-flocks/