Cirilla had mustered up a great deal of courage to approach her sister with such a bold request. This was the best solution that a young, green-eared girl like her could come up with.
Actually, if Cirilla had not determined the state of her sister's mind, she might not be able to make such a decision.
After all, Cirilla was only a princess who had never experienced the suffering of commoners. It was just like what we read in numerous novels - where daughters from rich families ran away from their houses in order to pursue freedom in love. Only rich daughters would actually find the necessity of eloping.
From the novel's perspective, a daughter from rich family might be able to obtain anything she wanted. In reality, she would quickly learn how difficult life was without the protection from her family. The stubborn ones might be able to stick to their plans. Others would quickly regret their choices.