Tail feathers gone

[Junkybird]

Hi, just went out to check on my birds, and one was on the roost in the coop. I looked at her and all but two of her tail feathers were gone and it was really bloody around the tail stump. I immediately caught her and put her in a small dog crate INSIDE the coop. I was going to give her food and water also inside the crate.

Would this be from another bird picking on her? Could she have done this to herself? I also have two ducks and 6 guineas (young though).

What should I put on it? Clean it with? How long should I wait until I let her out of the dog crate to join the others? Surely not until the feathers have grown back out?

Please advise, thanks.

 

[Junkybird]

I feel the need to add in more details.

This is an Americana, about 20 weeks old.

She may or may not be laying yet, I don't know.

There are two Mallards (one male, one female), 6 young guineas and 15 other chickens in this coop (two are roosters).

I searched before posting and realize that this is a common malady among chickens. My questions are:

How long should I keep her segregated?
How do I clean it?
What do I put on it?

Thanks