Is she able to get up move about and perhaps eat/drink on her own if she's with the flock and not be picked on by the flock?
If so, I'd put her with her flock and watch to see that she's staying hydrated and eating, just pull her aside to give the daily medications. Sometime being isolated is very depressing for them, so they just tend to sit and mope, often declining more.
Feather picking can be a bad habit for sure, pinless peepers may be one solution that you can try. Depluming Mites live under the feather follicle and feed on blood, my understanding is they are very irritating and the birds will scratch a lot, pulling and plucking out their own feathers digging into the skin to try to remove the Mites. Ivermectin is the treatment, so hopefully if Depluming Mites are part of the problem, those will be taken care of.
As for her face being darker, could that be dirt? I have some girls that get dirty looking like that after eating something juicy like tomatoes or watermelon. See if you can give her face a bit of a wipe/wash up and that it comes off.
Hopefully the medication will be helpful. If she's really bloated with fluid, then draining may also give some temporary relief.
