Transmigrating Into a Book: Bloodstained Nightingale

The modern-day assassin "Nightingale" transmigrates into a novel called "The Phoenix Rules the World", becoming Rong Shuang'er, the daughter of an official whose entire family was condemned to death after he chose the wrong side. To protect herself and her family, she decides to strike first and put her professional skills to use: she'll take out the male and female leads, all their helpers, and the villains.

Theme: The female lead stands on her own.