In Season 1, Cordelia respects Buffy just about as much as a lioness respects a tiger who has just wandered into her territory. She saw, for the first time, someone who was her equal, and perhaps a bit more, but who was out of her natural environment. With the home town advantage, Cordelia was a little apprehensive, but not really feeling threatened.
By the second year, Cordelia had seen just how powerful Buffy was, and certainly she could respect her physical power, but she knew beyond a doubt by then that she did have certain advantages over Buffy, especially at the beginning of the year. The advent of Angelus, and the chaos that he brought along with him was probably the first time that Cordelia had ever been directly affected by Buffy's world. Before that, it was something that she could just walk away from whenever she wanted to. Angelus changed all that.
In Season 3, "The Wish," Cordelia got to see first hand what Sunnydale, and her own life, could have been like if Buffy hadn't ever come to Sunnydale. THAT, I believe was when Cordelia Chase, Sunnydale debutant first began to actually appreciate, admire, trust, and unconditionally respect, Buffy Summers, Slayer.
And somewhere along the way, I believe that they actually became friends.
