That's great that you are making progress! I am sure she will tame and trust you eventually. It just takes time. Is she actually going closer to you, or just relaxing?
Of my budgies, all but my original hen were quite wild when I got them, and it took an average of two to three months to get them fully tame. Except for Arwen, who tamed in two days. But considering that she also tried to climb into a running shop vac on ore than one occasion (and had many other adventures besides) I put that down to an incredible amount of curiosity and no survival instinct whatsoever. And her babies all had a similarly whimsical view of the world... I felt I almost needed to sell the little nutters with warning labels or something.
Just give her time. Budgies are not as complex as the bigger birds in many ways, but once they feel that their trust has been broken it takes them a while to trust again.
It might be too that she has always been kept alone, and those birds do take much longer- the isolation just really does something to them. She needs to learn to trust, and the whole concept of interaction. I had one that had been kept alone for three years, and it took a long time to get through to her. Even after she would step up,etc, she was very much in her own little world for a long time.
Any more progress?