It will later be revealed but if you want mild spoilers...
Out of ignorance and lack of parental guidance, she consumed a herb (mugwort) to stop her menstruation because she thought menstruation is a disease and mugwort is a remedy for bleeding, it really helps with bleeding but should not be taken as a medicine because when consumed it acts like a poison that makes women infertile.
So she will never be able to have children ?
Well It's nice to know. And get out of the way some baby annoying plot.
Thanks for the spoiler :D
more spoilers if you don't mind
in the future this man who used to take care of the duke will give lucia's maid the cure to her being unable to give birth because that man was the one who care lucia the medicane to not be able to give birth
Ok "Bad Science Monday" I suppose. Thanks for the spoily friend :D
no problem
How do she know ? she never said it before ?