Although I understand your frustration, you will learn many variables come into play when a show is cast. It is certainly not a "talent" contest. And like most businesses, who you know can make a difference in getting the job. A dear friend often reminds me, this isn't "show-fun" it is "show-business."
There are times that pure talent with NO contacts prevails. There are other times that politics play a major part. This is true from community theatre to Broadway and we have experienced it at both levels. BUT, when the chips fall your way -- it can be a wonderful and enriching experience.
Just keep plugging along and know there is a part waiting for her.. Just not always a rhyme or reason to how it happens.