No Heir Despite New Children

[Coyutie]

So I had a weird situation which almost resulted in a game over due to no heir .I eventually changed the law to nominate a new heir, but would like some insight on why I was having the problem in the first place.

My PC king has 7 or so children but his 1 son and male heir dies so now his eldest daughter is the heir. Inconvenient, but fine. He dies and his daughter takes over and almost immediately after his wife gave birth to his son. Dissapointing, but fine.

My PC queen now has no heir? She has 5 children but I assume they were all from her husbands dynasty so I divorce and remarry being sure it is matrilineal. She is 40 and it says she has no chance of children, but I chose a bunch of fertility boosting things so she manages to have 3 children yet none of them are considered heirs???

SO. She has a bunch of sisters, nephews, nieces, a couple daughters, a son, and even a half-brother yet NO ONE is considered an heir? Why is this?

I eventually changed the law so that I can vote for an heir and I managed to avoid a game over scenario, but want to know why I was completely unable to have a normal heir.

Any input?