My GCC Missy, occasionally does the same thing...and i take it to mean that she's quite happy where she is and doesnt want to move

She'll also occasionally bite my daughter when she asks her to step-up...once again i take as her way of saying "no!". I try to give Missy the right to say no to things she doesnt want to do, but if i need to put her away quickly, i ask her again and she usually complies, and when she doesnt i gently grab her. This isnt an issue as she is very comfortable with being handed and being grabbed doesnt scare her or make her uncomfortable. Also, Missy has never bitten anyone really hard, so its not a huge issue.
Try making every approach of your hand rewarding....either with a treat, a toy or a scratch, or what ever it is that 'floats her boat'

The other thing you could try is offering her something else (such as a toy or treat) that keeps her beak busy while you get her to step up from your shoulder. The other thing is to just not let her on your shoulder....but this is easier said than done with a GCC...they can be fast, and super-cute, and good at getting what they want

good luck
