The story
Her sister tried on wedding dresses with the groom.
Ever since she saved her from wolfsbane poisoning, her Omega sister has used that life debt to run every part of her life, and the wedding is where it peaks. She picks the flowers, sets the theme, and stands there with the groom smiling at her in the mirror. Any objection gets met with the same line about who saved whose life and why she is always the villain. Fine. They can keep each other. She leaves the ring behind, goes back to her royal pack and takes the throne.