Update: I had to put her down tonight.
I am writing down some brief observations just in case it helps anyone else to come to a decision in these circumstances. The predator attack definitely caused bad nerve damage that left her unable to control her movements properly. She would never have been able to resume a normal life.
She seemed stronger on Thursday, had recovered from the initial shock (see above post) and was not complaining. She crooned at me each time she heard my voice. I fed her with a syringe every few hours. Her wound was healing OK (it did not look infected, no smell etc) and I continued with the Bactroban.
Today I realised I was mistaken about her eyes, she was only opening her left eye and not her right. I then figured that she might be blind. And although she could sort of stand, when I was feeding her, she was unco-ordinated and struggled to get into a comfortable position. Her neck swung down and to the left.
Today she no longer crooned when she heard my voice. She complained and struggled when I picked her up to feed her. I had to cuddle her close to hold her still and open her beak for the syringe. This afternoon she was looking uncomfortable and seemed restless. I fed her and decided that it might be time to let her go.
This evening she stated crying and thrashing around quite stongly and she was clearly in distress. I called my folks and gave her some rescue remedy in a syringe. My dad came round in half an hour to help put her down with sharp secateurs, he brought a security guard who was happy to have some meat to take home to his family. I cuddled her, carried her out and put her in his hands. They say she didn't struggle.
I noticed that a pigeon or dove had also been taken by a predator in our garden this afternon. My other girls have been confined to their coops, I am going to only be able to let them out under supervision from now on, which they hate.
(cross-posted to the Emergencies section, where I made a thread)