I mean, I’m not sure that it’s exactly rigged, but it is confusing and inconsistent.
Later, I realized that each time I redid it, the amount of questions and the questions themselves changed. From this, I added up that since each choice would make you lean towards a specific house more, the difference in the amount of questions and the questions themselves can effect your final score.
Same goes for the Patronus quiz, by the way.
So what I did is I kept on searching for a quiz that had all the answers that were included in the Pottermore quiz and the questions asked stayed the same each time you redid it. I eventually found one, I’ll provide the link here.
This one is more accurate, so tell your sister and your friends to use this one