It is usually only the first four or five of the primary feathers that are clipped, and the cut ends are protected by the primary coverts.The bird needs to be able to glide downwards safely but not get any lift.
A young Grey should have learnt to fly before the feathers are clipped so that they can build up their chest muscles and learn to fly and land safely. Any feathers that are trimmed must be fully mature.
The timescale for growing new feathers will depend on when they were cut in regard to the molt cycle - it could take up to a year for the new ones to start to grow.
It is difficult to say because they are all different with regard to activity levels. My Monty can't fly but he flaps his wings a lot and he is very strong. Mitzi can fly but she rarely does. Most parrots prefer to walk and climb rather than fly. Flying and landing is a skill that has to be learnt. The flight feathers will molt and be replaced gradually, they won't all be replaced at the same time, so as time goes on you should be able to see what happens and how she progresses.
Somewhere in another universe, dear brother, you got saved.
Sid's story on flying. He came to me as at 8 months of age, trimmed and never flew as far as I knew. Over time the wings grew in and I out of not knowing thought I should have them trimmed, so I did. Sid became very fearful of everything and could not fly and had a hard landing that I am sure hurt him. I was a new parent also and was learning. During my learning experience I read a book called ' For the love of Greys" and it helped me understand my best friend. I let his wings grow in, it took time.many months, and when he became a great flyer he gained much confidence. Now my story is not to say this is the way all greys must be. Many do extremely well trimmed slightly so that they will glide down gradually, they each have different temperament. Lets your baby teach you what he needs. Have many years of love.We have all been down your path. This is a great site to help.