I feel like she doesn't know how hard the kingdom has been hoping for a child with the first queen and her many 'pure-blooded' people...
The older you get the harder having a child is especially in those days. A 18 year old having a one night and has a higher chance of getting pregnant that a middle aged married couple who are constantly trying. You would need to have constantly been having sex in order to reproduce a child and even then sometimes you don’t (like how the 1st queen and her maids couldn’t get pregnant with the kings child despite having sex with him). That’s probably why she thought that she also wouldn’t get pregnant since the king didn’t come back to visit her.
And don’t even get me started on giving birth to a healthy child because it’s not uncommon to have a miscarriage or for a child to die shortly after they’re born.
But like they had sex and didn't take any precautions so... Wdym my accident, honey, why else would the King and her do it?? If not to have a child??