Bella's vet work is all clear and the vet thinks her matter is psychological/emotional/hormonal.

I personally am starting to think that this sudden behavior change was brought on by jealousy. I recently got a baby Hahn's, Lola, and her cage is next to Bella's. Lola is very sweet and gets lots of love and attention. She is starting to talk and even told Bella that she was a "Good Girl" when Bella kissed me through the cage bars. I think that Bella wants loving too but she just doesn't know how to handle it after all this time without any.

Yesterday Bella climbed onto my shoulder while I was reading on the couch and she didn't try to bite. She stayed approximately two minutes of her own accord. I don't know how we broke through this barrier but she seems to be getting better behavior every single day.

Oh, yes, indeedy, they are jealous little things! Sabu hates me because Tobita likes me, Tobita bites me because I pay more attention to Elvira than her, and Elvira bites me only when I pay attention to other birds so, yes, I think you hit the nail in the head on that one. But the behavior subsides A LOT (virtually disappears actually) outside of breeding season so, if you watch her light schedule and diet, she will get better and stay good until March.