Your narrow, petty, sectarian viewpoint on what is permissible religious expression (or prayer) in public is the problem ~
I happen to agree, basically, with SD on this; if I wanted to go to a revival, I'd go to a revival.
If a speaker wants to invoke God or Jesus, fine; but asking people to convert is a bit much. It could easily be the case that next year the valedictorian is Muslim or Buddhist or something else non-Crhistian. But there's no violation of the law here, IMO; I think the poster who said she was glorifying herself, or showing off, is right.