
as far as I understood, the queen (Patricia) is infertile and the mistress (Rosemund) took advantage of that. By using her power she made it so that Patricia would be queen. An infertile queen means that the first child born will be from Rosemund aka no worries to lose her position. If Rosemund produces an heir she has much more reason to become the empress.
Ofcourse this is what Patricia must avoid at all costs :/ Idk if she really is infertile or not, kinda hope it isn't true

During the health test, the doctors would examine all the queen candidates. Rosemund used her connections to figure if there was a weak candidate. That's how she found out that Patricia is infertile and thus she made the emperor choose Patricia as queen. She also made sure to get rid of (aka kill) all the doctors so that no one else would know about the infertility except herself.

I thought that Rosemund just had the doctors sabotage the test or some shiznit. Like she bribed the doctors to frick up the test and killed them to hide any evidence. It doesn't seem practical for the author to put the main character in a position to lose. So the probability of her actually being infertile seems kinda low.
I'm a bit lost honestly, partly because the names seem to change from one chapter to another (maybe its because of the nicknames) and I really can't understand the whole infertility thing