I just spent almost $500 to save my chicken, but now it's acting weird... what is going on?

I had to combine my shy chickens with my flock as we are moving and will no longer have a greenhouse and a coop. I read up on it, but some toys, treats, crickets etc. I let them in a larger fenced area for a few hours and stayed to ensure nobody was hurt. The next morning I let them out and found a silkie hanging back. They teamed up on her, she had no feathers on her head, her skull was exposed, and she was covered in blood. I scooped her up and rushed her to an ER after hours vet on Sunday. They kept her overnight and gave her antibiotics, anti inflammatory and pain meds. Then they cleaned her and closed her wounds Monday.

Monday night we brought her home and kept her inside, we also brought in the other silkie as she was getting picked on. Monday night we noticed the white silkie was doing weird things with it's head and neck, just acting off. It's Tuesday and the grey silkie that has stitches is opening her mouth while she stretches her neck up, she also is closing just one eye and seems so tired her heads droops really low.

I don't know what to think, she took such a beating that I want to chalk it up to that. But the white silkie didn't get hurt like her and is acting strange too. Did I just spend $500 on a chicken that's dying of some disease? Is there anything else I can do to save her? What do you guys think it is?