She does look like heck and the frizzle may be playing into some feather brittleness. That nor mating wouldnt explain the feather loss and red skin on the front of the neck.. I would consider treating for mites/lice, etc. if you haven't done so already, and NOT using DE.. which messes feathers and skin up more.
It's possible crowding was part of the problem.. but things get out of control quickly AND easily missed in large numbers.. even the best of keepers.. may face (internal or external) parasites if their birds ever see the outdoors.
Do you know what their ages are?
Some feathers may not grow back until molt.. and that is fine.. but skin quality should be greatly improved.. with NO scabbing or angry redness.
Do you have other birds already?
