I am not certain what exactly attacked her, it could be anything. I can tell you that with our experiences with hawks they usually go for the head first, ripping it clear off.
To treat her, you will likely hear different things from different owners. We have had several predator attacks (hawks, foxes, coyotes, dogs, raccoon, possums, you name it), and generally treat them the same way.
- Pull her inside, away from the rest of the flock (you have already done this).
- Check her thoroughly to analyze the wound(s). It looks here like a surface wound (i.e. it has not hit her lungs or any other vital organs). You will want to make certain there are not any other superficial or puncture wounds somewhere else on her body. Attempt to cut any broken feathers away from the wound so you have enough room to see the entire wound, with about a quarter of an inch area around the wound.
- Clean the wound with water first if there is a lot of grit and dirt, and then hydrogen peroxide. You may want to have someone with you to help you with this process. I normally take a large bath towel, and wrap them snuggly with their legs up against their body as if they are sitting on the ground. I wrap the towel lightly around their head, putting their head lightly down under their wing, and then open the area of the towel where the wound is. The water will likely not startle them if it is room temperature, but the peroxide will. If they are not snug they will end up flying around the room.
- After the wound is clean, if it is superficial, we dress it with Red Kote (scarlet red oil, not the aerosol, the type with the dauber). Red Kote does not dry stiff, it will remain pliable and leave the hen's skin soft while it heals.
- Keep her separated and inside overnight (if possible). If she is acting just like a hen, it may be okay for her to go back to the flock, just make certain no one else is picking on her, and attempt to keep her from dusting the wound. It is very difficult to keep them contained when they are hurt, but don't realize they are hurt.
- Give her a bit of a feeding boost with extra vitamins. Depending on the injury and the bird, we use a mixture of children's chewable organic vitamins, Sav-a-Chick electrolytes, yogurt, and sugar water. Not all at once, but over the span of time it takes for them to heal.
- Keep an eye on the wound, if it starts to look worse instead of better, you will want to slip a bit of antibiotic into her sugar-water or in apple juice. We usually start with Corid (amprolium) and gauge the response.
- Don't keep her eggs during this process. If she is okay, her eggs will look normal. If she is not, you will notice smaller, or misshapen, or thin-shelled eggs. Keep an eye on her until her eggs return to normal.
I hope this helps.