These are Coturnix Quail? Sometimes they see things you can't and if this hen is sick, they can gang up on her and try to drive her off. Also, if you don't have enough room, at some point, and this can be months later, they can all decide that there is just too much competition and try to drive one of them off.
So if this was my bird, I would make sure she isn't sick or anything. Make sure she is not too thin either which would indicate she has worms. Then I would double or more the space they have. Add another set of feeders and waterers. Put in fake foliage for them to hide in and feel more natural.
I would do all this right now and get her back into the group as fast as possible. The more time she is away from the flock, the more likely they are going to pick on her again. So spray some blu-kote on her wounds so that nobody sees them. This stuff will also help to fight infection while it hides wounds. It is purple in color and stains. So use gloves on your hands and apply it with a Q tip to her wounds. And get her back into the flock after you have done all the rest of this stuff.
If after you have given them more space, added some hidy brush and added more food and water and they still pick on her, you can either remove the bird that starts this entire thing or keep her separate completely.