With Mimi and her issues, the hard part was mostly just being patient enough to let her realise that no one was going to try to force her to do or not do anything, that she was free to make up her own mind. It was harder in the very beginning due to the nearly non stop screaming. It was both nerve wracking and very painful on the ears, which made self control very difficult. She has done all of the real work.
All of the birds that I have came with their own baggage as they were all unhappy with their previous life situations, Most of them just needed time to heal and to allow some of their memories to begin to fade, Kiki was the other that was the most difficult for me due to her biting Which took over a year to change and she is the one that ended it after testing me to see if I would trust her despite all of her biting of me.