Again, that happens to be your narrow, sectarian religious belief ~ I don't happen to share it.
If you believe that only a secularist would find this inappropiate, then it is you who has the narrow view. High School graduations are not the place for a tent revival or for any type of attempt at religious conversion. A prayer or a part of the speech being used to explain how religion played a factor in her success would have been OK. But, I think sometimes people pull stunts like this to pick a fight.