Well, I guess it's obvious that the schools are going to be our political battlegrounds for the foreseeable future...
OK, a few days ago, septbride2000 posted a thread about a school newspaper that was censored from publishing an article with interviews from gay students. In this case, as I remember, most of the conservative posters said that it was the principle's decision and we shouldn't question his right to make decisions as he say fit regarding the wellfare of his school.
So, why isn't this principle being given the same consideration here?
Personally, I'd be fine with the girl singing the song. It's what she chose to express herself, it's not part of the school curriculum, it's fine (terrible song, IMO, but if that's the way she wants her school colleagues to know her, fine. She'll have to deal with the aftereffects. Kids are brutal when it comes to talent shows...one kid in our school sang something from "Oliver!" and he never lived it down). So, just as I supported the rights of the lesbian/gay students to tell their stories in their school newspaper, I support this girls decision to sing the song she feels best expresses herself.
As the OP mentioned before, music is an art, and if schools are going to censor all religious art to cover their butts, then students will be the poorer for it. A good portion of the Western canon of art is made up of masterworks with religious subject matter. I think we are selling both students and teachers short when we assume they can't study this type of material without it becoming a sermon.
Essentially, I think certain political elements have raised religious debate to such a fevered pitch recently, that reasonable responses to such situations have been thrown out the window.