Just a quick update now I've had some time with her.
She is a lot better looking now after a few showers, I think this has improved her mood too as she is a lot more energetic! So far she LOVES toys, you wouldn't believe this is a bird who had none before. She gets into anything I put in with her and much to my relief she doesn't seem to be picking as much (or not while I'm around anyway).
I have her booked at an avian vet for next weekend, it's absolutely miles away but there isn't one by me

I actually spoke to a rescue center here who are used to handling problem birds and they said it could be internal mites as they tend to hide out in the ears which could be what is causing the plucking around the face. He said she could have caught these if kept in dirty conditions, particularly if exposed to cats.
She is also a pretty good eater, although she only eats a very small amount she will try most things which is odd as they guy I got her from said she wouldn't eat much but a little seed. So far I've been feeding her mixed fruit & veg plus mashed swede/carrot mixed with red palm oil to give her lots of vitamin A. Another good thing I noticed is that she is producing a lot more dust now, when I first got her the feathers felt kinda hard and brittle not the usual Too talcum powder soft, they are much better looking/feeling now.
So it's looking up for now, I'm almost hoping she does have mites so at least I can get to the bottom of the plucking.