The Emperor’S Favourite: The Special Agent And Abandoned Concubine summary:

Dong Yan crossed over and became the Fifth Miss XiuYan, the trash of the Dong family. In this world, she's being sought after by a vicious sister and many scoundrels. Fortunately, she remembers her skills of being a secret agent from her previous life. Turns out the original master had crippled spiritual roots… How will XiuYan fair against her bullies with her current abilities!? Who is this person that suddenly appeared to protect her?