If I remember correctly they checked everyone's fertility in the health check and the doctor either got it wrong or lied to Rose that the FL was infertile and apparently that was one of the reasons she was chosen as queen so she would be kicked out for Rose to take her place because she wouldn't be able to produce an heir.
Wait... How did they assume she can't get pregnant if they didn't even have sex. Wtf is wrong with those people. ಠ◡ಠ
During the health test deciding a queen, they actually checked her fatality
Fatality or fertility?
If I remember correctly they checked everyone's fertility in the health check and the doctor either got it wrong or lied to Rose that the FL was infertile and apparently that was one of the reasons she was chosen as queen so she would be kicked out for Rose to take her place because she wouldn't be able to produce an heir.