I don't think you do get the point as you are stil saying "But she is probably" ..... you are being prejudice! You are judging someone on how they look. You obviously don't like people to do that to you - so why do it to others?
The way someone looks does not tell you who that person is, what they are thinking etc. This isn't the movies, the goodguys don't wear white and are all handsome, and the bad guys don't all wear black and are ugly. If you think you can judge on appearances - you are not only guilty of being just as big a bigot, but you are also at worse risk of being duped.
My Grandfather is a narrow minded bigot. He judges on appearances. Consequently we have rowed in the past as hewould look down on friends who are really good people, just because they wear 'unconventional' clothing etc ....... consequently - it was really easy for a well spoken, smartly dressed man in a suit to rip him off.