The main Halloween costume:
Yes. She is a Star Trek captain, specifically, the command gold form the original series. I believe that by the time she is old enough to be the next captain of the Enterprise, they will switch back to gold because it is flattering for her skin tones.
There was also this costume:
Because it was cute, that's why.
In sequence: Finding candy, grabbing candy, results of candy being taken away.
Lastly, greeting people at the door:
She's either going to be just like us, or need years of therapy.