@cervidae
From the looks of it and 5 minutes of looking back chapters, she just so happened to transmigrate by a stroke of luck(?) and is changing the plot. And according to the lil hamster, changing history or plot to something beyond what was supposed to happen is dangerous and has serious repercussions down the line, which our MC is to prevent, among other things she needs to do.
@Faryshta
If you're talking about the first part/act/life(?) then IIRC MC thinks she's foolish and naive because the girl somehow falls in love with her target of revenge (dumb girl somehow died and reincarnated or returned back to her past after dying because of the Emperor). For ancient Chinese dynasty, it was common for Emperors to have a harem, because lfie happens and things can happen life the Empress getting poisoned and becoming infertile, or being unable to give birth to a son, or the Crowned Prince dying, etc. A Harem was a way to deal with these issues. And in a Chinese harem, there's one Empress (or Royal Consort or whatever) that is equivalent to being the Empress, granted by the Emperor, who is expected to give birth to a son to be the Crowned Prince usually, unless something happens.