Her "best friend" (that was the description in all the press) most certainly is a relevant witness. Kavanaugh denies the party with those people ever happened. Ford claims it happened and she was there. If the other people allegedly at the party deny that, there could not have been any attack, the whole story falls apart.
The only reason this has not yet been universally acknowledged as obvious is that people are emotionally invested, they dislike the guy in the story and liked the woman.
Let us be clear: Ford is too afraid to fly in order to testify about a serious allegation she chose to make, one that managed to further split people across your whole country. But she is not too afraid to fly for pleasure, for vacations, for family issues, or for dating. The other hypothesis is that she made up the fear of flight in order to delay.
You choose to believe her because you wish to believe her.