The Queen's Advice
According to the initial plan, Queen Nadia was meant to be incapacitated by the poison in her system.
The poison was meant to slowly consume her organs, eventually leading to kidney, lung and liver failure. She was meant to be hospitalized and placed on a life support machine until death came calling.
Princess Rhiya wanted the old king, -who had simply refused to die or give up the throne,- weakened and distracted by the queen's sickness. She wanted him out of the way so that Prince Tristan could take up his responsibility as the rightful heir to the throne in the absence of a dedicated leader.
But unfortunately for them, Amir showed up with a temporary solution for the queen. He provided a poison suppressant that could delay the effects of the poison long enough for the Queen to enjoy a few months of blissfulness and healthy living.
But sadly, all good things always come to an end.