Abandoned at the Altar, I Married the Godfather

Her parents were killed when she was a child, and she was sent away to live on a mountain, the only heir the family had left. Years later she comes down to take her place in the house. The people there treat her as a spoiled girl who is good for nothing, and her fiancé breaks off the engagement. None of it moves her. The useless heiress is a disguise she keeps up because she means to reach whoever had her mother killed. When that person starts moving where she can see him, she drops it. She is a witch with dragons at her call, and she sets them on the people who come after her. A marriage into the royal family is put to her and she turns it down. The girl who has been passing as the family's daughter has been working against her the whole time, and she takes her apart. Her four brothers, each of them a power in his own right, kneel to her and serve as her knights.