I Got the HEA Script After Reincarnating as Cannon Fodder

When Gu Xiaowan opens her eyes, she's dressed in a bright red wedding gown and has transmigrated into the role of a murderer, and not just any murderer, but a disposable supporting character in the novel A Dream of Terror. After barely surviving, she keeps getting dragged into strange case files. All she wants is to stay alive. So why has she ended up with the protagonist's script?