Lady Sundown (#1 of the Danner Quartet)

As beautiful and reckless as the glorious Oregon wilderness, Lexie Danner was determined to claim the shining promise of her future. Not for her the stifling confines of an elegant finishing school—she would fulfill her dream to be an animal doctor, and wed whom she pleased! No one would stop her—least of all her so-called stepbrother Tremaine. Related to Lexie through marriage only and her enemy since childhood the rugged, boldly confident young doctor sparked a fierce anger in her—and a sudden, newly-awakened desire.
But a scheming land baron's conspiracy and a powerful, vengeful enemy from the past threatened to destroy all they both cherished. Now they would be forced to fight for their fives—and a love as blazing and eternal as the boundless mountain skies...