Zahras the sholder sitting is really a personal choice just like having your bird clipped or flighted. Zahras does this with you not just because you are soft on her but because you are her one. Alex will step up for anyone in the house but only wants to sit on my sholder. You are mom and she will do for you what she wont for others. As long as you have a trusting relationship with her there is no reason that she can't ride on your sholder. That is if it is something you don't mind. I can't imagine not having Alex riding around on mine.
As for keeping her busy that is easy. You can work on teaching her tricks. There are some great trick books out there. I have also worked on teaching Alex his colors. He knows red, purple, and yellow so far.
Here is the link to the Alex Foundation (not my Alex). Alex was a truely amazing grey and all of our greys have the potential to be just as amazing.
http://www.alexfoundation.org/