Hi and welcome to the forum! well done for giving this birdie a home, well what type of seed mix is very important as pet shop mixes are no good you have to buy online, mine get tidymix and AS30 if your already feeding this great if not its a good idea, chop is a great way of getting veggies into birdies and I have converted a few seriously non veggie eating sunflower seed junkies onto it, it takes time and for you to not give up even if it seems wasteful in the beginning, start off with 50% chop and 50% seed and gradually change the ratio until no seed or just a bit, here is a link to chop
http://www.melbournebirdvet.com/chop.aspx then if your bird is on a seed diet it will need supplementing with nutrobal to make sure they are getting everything they need nutritionally, this doesn't need to be given everyday and it is especially good to give fussy eaters but all my flock get this a couple times a week sprinkled on their seed, you will notice a massive difference in her once you start doing this, also greys need something like this as they require extra calcium in their diet so you will need to make sure she is getting this, also how you feed makes a difference, my lot get chop in the morning when they are most hungry, then fruit and other things like palm oil on toast, (palm oil excellent for greys) scrambled egg, bird friendly muffins whatever I have made or want to give them for lunch and then in the evening they get their seed, if I leave the seed in all day they will favour this over the chop so again another way of getting them to eat, as Julia mentioned an avian light is a must as it helps them process calcium, making sure she has foraging toys to keep her occupied and mentally stimulated, we have a foraging thread you can look at for ideas, and you must get her to a vet to rule out anything, sometimes they pluck because there is something going on internally, if all these things are sorted and right you will have a very happy and healthy grey and in time one who may stop plucking but then again she may not and that is something you may have to come to terms with but your grey will be a very healthy and happy bird which is the most important thing, there is loads of helpful advice so have a good nosey around and we are here to help, if you need any help with where to get anything just say