When she first laid her eyes on Sasha winterchild, Cortana believed the younger girl to be the one who would bring about her destruction. After all, the first time she met Sasha, she was reminded of her younger self.
She resplendent with innerlight.
Thus, Cortana had been extremely cautious in dealing with Sasha, very covert, and gentle as she tricked the girl into her own father.
Edward indeed had given her time of a day, but Cortana had not known where he was getting forces to apprehend her, nor did she know how he planned to block her father.
It had been Sasha's words that helped her oppress her father. Sasha Winterchild, ever so gullible, and utterly believing what her nanny tells her, was really obedient and loyal to her in-laws. When her father wanted to put her on a ship back to winterland, she had rushed to Cortana to convince her father of the idea.
