The explanation in the series why she binds to Cleon is not canonical... so we can't be sure the zeroth law will be part of the show. In the books, this law is the reason Demerzel lead (in the shadows) Seldom to create the psychohistory. She needed parameters to decide what's best for humanity.

According to the Asimov cannon, Demerzel was the second robot to derive the zeroth law from the other 3. According to zero law, A robot may not harm humanity, or, by inaction, allow humanity to come to harm. It means that if a humans or even a group of humans represent a danger to humanity, a robot may disregard the 3 laws.

In Robots and Empire (1985), R. Giskard Reventlov, a robot with the ability to read and influence human minds, formulates a new principle, recognizing that the survival of humanity as a whole is more important than the well-being of any single human. He reprograms another robot with his abilities and laws, R Daneel Olivar... who later would become Eto Demerzel.