There are a lot of reasons why a Grey can begin to pluck and sometimes it can be difficult to figure it out. The first thing you should do is take her to an avian vet to rule out any physical reasons.
As Dave said it could also be a reaction to stress. Moving the cage, ect. How much sleep does your bird get each night? How much out of the cage time?
Also things like pollutants. Cigarette smoke, air fresheners, candles, cleaners,
The trip to the vet is the first step. If they are ill or in pain it will cause them to pluck. There is a member here whos grey was plucking until they discovered an ear infection. No symptom but the bird was in pain and they did not know it.
Good luck.