Our hearts go out to the high schooler who walked into their coop and found a rooster they raised doing serious damage to an older hen. That's a brutal moment. You raise a bird from a chick, you think you know its temperament, and then one day it turns on a member of the flock. The hen has swollen eyes, a bare head, and isn't standing or walking yet. The owner cleaned her with Vetericyn and Blue Kote, separated both birds, and is hoping for the best. We've been there. Or close enough. The helpless feeling of wanting to do more when your wallet says "no" is a special kind of stressful.
Here's the honest take: If your hen is sitting up but not standing or walking, that's a bigger red flag than the feather loss. Head feathers grow back. Swollen eyes can heal with continued cleaning and time. But a bird that won't put weight on her legs could have internal bruising, a pelvic injury, or even nerve damage from the attack. The owner is doing the right things with wound care and separation, but the hen's refusal to eat much and her inability to stand deserve a second look, even without a vet. We'd suggest offering her scrambled egg (cooked, cooled, no seasoning) or a bit of wet chicken feed. High protein, easy to eat. See if she pecks at it. If she still won't stand by tomorrow, you might need to consider quality of life. That's hard to hear, especially when you're young and already doing everything you can.
What we'd tell any reader in this situation: Don't blame yourself. Roosters can turn without warning, and a flock pecking order can get violent fast. You did not fail this hen by not predicting it. But you can learn from it. Once she's healed or if she doesn't make it, that rooster cannot go back with the rest of the hens. He's shown he'll attack a hen who can't defend herself. Some keepers will rehome a rooster to a farm without hens. Others will cull. Both options are valid. Neither is easy. But letting him back into the flock risks a repeat injury that you might not catch in time.
Right now, focus on the hen's comfort. Keep her in a quiet, dark place. Offer water with a little apple cider vinegar (a splash, not a soak). Check her eyes twice a day. If she starts eating and eventually stands, celebrate that small win. If she doesn't, take it as a hard lesson in the part of chicken keeping nobody likes to talk about: sometimes you can't save them, and that's not your fault. What you can do is make sure the next call you make, for her or for the rooster, is the one that stops the cycle.