Miranda and the Warrior by Elaine Barbieri

Miranda, the only child of a U.S. Cavalry major, has grown up in a very protective environment, yet still remains fiercely independent and stubborn. Shadow Walker is a respected Cheynne Warrior, with a reputation among not only his people, but the U.S. Cavalry as well. While out riding, Miranda is taken captive by Shadow Walker. During Miranda's captivity, she and Shadow Walker become closer than either of them imagined.

Part of the Avon True Romance series

Ok- not the most realistic or believable romance I've ever read, but I think that's part of what I liked about it. For the most part, until the end the romance was low key, and the story focused more on the characters getting to know each other and learn from each other. The ending was extremely abrupt and left me with a lot of questions, which I did not like.