Her whole thing is that she( and her rival who we see later ) are master manipulators and like to plot to high heaven.
This is because she herself is weak from a incurable diseases that have yet to be mentioned and the only way to survive in this world is to stomp your opponents 10 feet under or do it the sneaky way.
She came to the city because of a power struggle in the palace, but dont really care about how it ends.
but because of the king it's going to get even more messed up now as you are soon to find out...
She isn't really the MC´s enemy however, it's the prince (and one of his brothers) that she saved out of obligation to the emperor who is going to fuck him over the most.