Question about gay people in Christian schools?

Well this whole thing started when i told my mom i saw two girls making out at a football game. After i told her she said thats why my sister is going to a Christian private school. I then said what makes you think there will be no gay people there and she said they would be expelled. I basically said they can't do that just because they're gay. Sure like if PDA is against the rules they prolly could, but if they dont and are just a gay couple can they? So am i right or is she right?