Injury and Integration

I got a flock of pullets a couple months back. One of the olive eggers had a spot on her tail feathers but I didn’t think too much of it. I went out one day and all her feathers were gone and she was bleeding. Immediately separated and cleaned her wound. This has been 3-weeks. Her tail feathers are very slow to grow back, and every time I try to reintegrate her with the flock, they go after her. I’ve kept her separated, and she seems very stressed. She constantly paces her enclosure and rarely eats and drinks. The other birds have gotten much larger and she has not. I’m at a loss of what is best for her.

Any advice for what to do with the poor baby?