She was a useless Omega who didn't benefit her father, the Alpha of the pack. Until he wanted an alliance with another pack, and all their Alpha wanted was a mate. So, her father arranged for her to mate with the other Alpha.
Only she went from being ignored, controlled, and bullied to being controlled, abused, and a prisoner. Her father knew about the other Alpha's reputation, but he cared more about power and control than his child. His pack didn't seem to agree with his ways, but they were too afraid to challenge their Alpha.
She suffered the abuse in silence, and her new Alpha made her a servant whenever he had events for the packs.