The Cannon Fodder Didn't Die on the Road to a Political Marriage

Chu Jianuo spent ten years after transmigrating into a book before realizing that was what had happened. The male lead in the book was none other than her own older brother, the Second Prince of the Great Qi Empire, while she was merely a cannon-fodder princess who would die on the road to a political marriage at the age of fifteen. The book also featured a major villain who sided with the Third Prince for the sake of his own beloved, only to jump off a cliff and kill himself after the male lead claimed the throne. And now Chu Jianuo was already fifteen: ???