Defiance question

I don't remember the name of this book or its author, but I do remember that it's a book series. It's set in a medieval setting. The main character is this very tough princess, and she is engaged to this prince from another kingdom, and they are in love but then on the night of their wedding, the prince gets kidnapped. So the captain of the knights of the prince's kingdom (who is also the prince's half-brother), sets out to find him. The determined main character isn't going to let him go alone so she goes with him. I'm pretty sure that the half-brother likes her, and then they go together, on one horse, and pretend to be a married couple and stay at a kind of old couple's cottage for the night. That's all I remember. It's kind of like the book I mentioned above: Defiance, but this book is set in a more medical world.