I think the reason why was because of her dreams about the old count and their possible abusive marriage. She was young, immature, scared and traumatizes. If I was in her position I would also have the thoughts about infertility and what will the possible future of the child, terrified and scattered inside.
I know the reason why. That's not what this post is about. I merely stated that I kind of wish her "infertility" wasn't curable. Part of the reason for their marriage was that she can't have kids. It just feels like a copout to say "Oh, I can cure myself whenever!" A part of me wishes that she'd learn to find happiness as a mother with Damien, and not require a child of her own womb to get that feeling.
Oh I get it, apart from it was the bloodline of the lords. If no one, apart from Damien, is born. Then their line will be at risk in the future. But I still understand your conclusions. They will be lovely together, all three of them.
So, I kind of half wish that Lucia couldn't be cured of her infertility. There are a lot of women out there who can never have children, and it would be nice to see Lucia find peace, happiness, and love with her adopted child and realize she doesn't need her own flesh and blood child to achieve that. BUT, I know that's not how this is goin to go. She obviously cares for Damien, but it's also obvious she's going to get pregnant by the end of the story.