
More spoiler:
But as it turns out Trisha’s baby’s isn’t Souvenir’s in the first place. And, initially both Souvenir and Navier ate the possibly infertility inducing cookies and since they haven’t had a baby for so long we know one of them is probably infertile. And since Navier is our main character who deserves to be happy I’m guessing it isn’t her.

I don’t think so. If you look up spoilers for the remarried empress on the novel updates forum there’s a discussion about it and from that I gather that the child isn’t Souvenir’s. Either way, Navier has to be happy as the main character and if she’s infertile she’ll still end up facing the same problem despite Heinly’s love.
SPOILER!!!
-
-
-
-
-
-
-
-
-
-
-
-
-
So Souvenir actually made Navier infertile, it was an accident, but what made it bad is that he never confessed of it, not even to the latest chapter of the novel. So as he did, he took in Trashta and made her pregnant with his baby. Then, he planned on divorcing Navier to make Trashta empress and the baby a royal (as concubines' children cannot be considered royals, he had to make her empress). He plans on making Navier empress again after a year of letting Trashta become empress, finally having an heir to the throne, which is Trashta's baby. Of course, Navier knew nothing of his plan, only that she knew he was gonna divorce him, and so he came up to Heinley, the (currently in latest chapters) king of the western(?) kingdom. She asked him for a more of political marriage, and so Heinley happily agrees, as he had fallen in love. It just annoys me how thick-faced psycho Souvenir really thought Navier would sit back for a year and wait for the emperor to bring him back, like, no. She's smart and independent, and will think of ways to not be brought down, so like, piss off. Kindly.