Wise words from Violindad, who lives at the other end of the podium and has a double perspective: "Some voices are better for demos for freshman whose voices are still relatively immature. When I have asked students to demonstrate for younger students, I have usually chosen students whose voices are ones that a younger student can reasonably emulate (i.e. I have asked a student who sings well but has a relatively immature voice). I don't necessarily ask the best voice to demonstrate--it would harm young voices if they attempted to sound like someone who has a sound that is 5 years beyond them."
Whereas your D felt passed over and (naturally) humiliated by her teacher's, the motivation for the choice may have been unrelated to his or her perception of her talents or accomplishments.
I hope she feels better soon!