After Meiling, Nihuang investigates and figures out what happened and 1) she realizes that the Emperor is angling to destroy the Mu's if she doesn't do something first 2) she wants to avenge the Chiyan army by killing the Emperor.
With that ambitious goal in mind she, indirectly, sets herself up to marry the Emperor, giving the Emperor a false sense of controlling the Mu's using Nihuang as his 'hostage'. She gets herself pregnant with Jingyan's child, so as to fool the Emperor - apparently not as reproductive as he used to be?- into trusting her, and then slowly poisoning the Emperor... and her own self as well, since there is no other way the paranoid Emperor will eat the food if she doesn't first.
She plans to die before herself or her child is born and there is a moving scene between her and Consort Jing when she tells the Consort that she is sorry to do this to her first grandchild, but that Jingyan will surely give Consort Jing many more grandchildren.
Then, of course, Mei Changsu appears. And there are multiple plots and counter-plots involving murders and attempted/misguided murders (as the other consorts and even the Empress are envious of Nihuang's high position in the court.) Still work-in-progress so I can't tell you how it will end but I suspect, given Nihuang is badly poisoned at this point and even MCS seems helpless to stop her, that it will end well in the sense that Nihuang will triumph, but probably also die.