The girl was not authorized by the school to do what she did, and the school could not legally have authorized her to do it. It would be different if the school had announced in advance that students of any religion (including atheism) were invited to participate in a function where they could proselytize the audience. Then the school would have been treating all religious beliefs equally, and there should be no problem with an event like that. But that's not what happened here. How would you like it if you went to your child's public high school graduation, and the program included one prayer only, which was a highly sectarian Muslim prayer, capped by the student inviting the audience to join her in reciting the words that constitute a conversion to Islam (which per many brands of Islam, is irrevocable under penalty of death)?
What part of "strict neutrality" do you not understand?
BTW, we had to have the Baccalaureatte service in a Roman Catholic Church since some stupid damned judge around here ruled we couldn't do that at the highschool even if it was strictly voluntary and done outside of normal business hours and even if we paid rent for the building.
I considered it a horrific imposition on my rights to have a federal judge force me to go into a Catholic Church simply to make sure my son got full benefit of all the ceremonial aspects of his graduation.
At that point I decided that public schools as they are understood in America are a totalitarian artifact that should no longer be tolerated.
BTW, the RC's caused no problem. In fact, I knew most of them, and had done government business with several of the priests in attendance. I would imagine we all had the same thought on the matter.