Why does my teacher hate me and her?

ok so i have this one teacher and she loves me and she is always nice to me and all this stuff but she despies my friend. she gives her dirty looks and hates her to death. she is always mean to her and hates her so much. she loves me so on wesenday me and my friend planed it so that i would come into that teachers room when she that cl is over and when they were switching cles and say very loundly "laura your my best friend" so that our teacher would here me say that and maybe start likeing her and laura was like "kris your my best friend" and our teacher looked at us and we went back to our next cl. then later when i was in her cl she gave me a 2 hour dt when she said i was talking in cl which i wasnt so next friday i have a 2 hour dt but she would of never did that to me before that happened and she hates me a lot now and treats me like crap. why does she hate us. and she is not an old teacher. she is young. thanks