BEAUTY Of course, Niki Keene had followed her sisters 1 to Hard Knox, Texas--the Keene triplets were inseparable. And yes, she helped run their fledgling dude ranch. But when the townsfolk entered her in the Queen of the Cowgirls contest, she had to laugh. How could you be Queen of the Cowgirls when you were terrified of horses? Besides, she was sick to death of being "the beautiful one." AND THE BEST She wasn't laughing when hotshot cowboy Clay Russell launched an all-out campaign to change her mind. He was so sexy and so persuasive, she figured she was doomed one way or the other. It was either ride and rope--or lose the only man who'd ever made her glad