Based on the drama, that the only think that she hold so that she can keep being sane because she lose her freedom. after she became concubine, she cannot leave the palace, stuck there until her died and based manga, need to be respectful to his son because his son in higher position from her. Her life totally changed. So she held that, so that she still not lose everything.
Not manga but novel
Spoiler
She give a hints to King that she love him so much but the King do not realize and understand at all until they meet again at afterlife
Why won't she tell the king she loves him.... Hmm?