This episode is about Elizabeth Bathory aka The Blood Countess, who is known as one of the most prolific female serial killers.

Sources:

https://www.history.com/this-day-in-history/december-29/bathorys-torturous-escapades-are-exposed

https://www.britannica.com/biography/Elizabeth-Bathory

https://www.nationalgeographic.com/history/article/the-bloody-legend-of-hungarys-serial-killer-countess

https://www.historyhit.com/the-blood-countess-facts-about-elizabeth-bathory/