The power structure within a modern rich and powerful family was not unlike that of an imperial harem. Everyone nursed their own aspirations and goals, plotting and scheming against one another.
It was her belief that no matter who Mubai eventually married, she would not love Lin Lin from the bottom of her heart.
She would have ostracized him or, even worse, harm him.
After all, Lin Lin was Mubai's eldest son so he had the strongest claim to Xi Empire. He would have to be removed for the other woman's own child to rise to the top.
Therefore, after Mubai remarried, Lin Lin's situation would be dangerous and precarious.
Thus, she had to lead him away from this environment, to help him avoid all these power struggles, and for him to be independent and strong.
However, she couldn't reveal all of this to Mubai…
If they knew she was dying and purposely hid that fact from them, it was certain that they wouldn't let her take Lin Lin away.