This could get messy

There's 2 things Arista can do. 1 is that she can take her place as house Monique 54th heir. That would mean the would be like her dad. This would also leave jiun as the empress. Jiun isn't capable of being a strong empress. She is relying an hour of Zena and they are using her, so her vision of the empire and emperor would be screwed and cause problems during her rule. Plus everytime one of her plans goes wrong she blames Arista, meaning she doesn't take accountability for her actions. These are not good qualities an empress should have.

2 would be too become empress. This could lead to jiun becoming queen. This would happen because there's rumors that Arista in infertal and can not bear children. Arista wouldn't have support od the nonimperialist since thier support is with jiun. However with the emperor's support she could have some influence. But until she has a kid there will be problems of whether she should be empress. Also her father will have no heir for his house. This can cause problems for him later.

I don't know of a third way where she can take care of house of Monique and be empress. Its impossible. If the author is gonna make endgame Arista and the emperor then its gonna take some miracles and that would also mean some of my predictions were wrong. But if not phe will be the official heir to house of Monique and may end up with cairsen.