It's tricky. 'Kept Woman' could be based on a real situation, but it might also be a completely fictional creation. Without more information, it's difficult to know for certain.
It's possible. Sometimes such stories come to light through personal accounts or investigative journalism. However, determining the authenticity can be challenging.
It could be either. There have unfortunately been real - life cases of human trafficking which may involve elements of such horror, but there are also fictional stories in the realm of horror or thriller literature that might explore this disturbing concept.
I'm not sure specifically which 'woman kept as breeding slave story' you are referring to. There could be many fictional or unfortunately real - world historical accounts that might fit this description. It could be about the inhumane treatment of a woman forced into a situation where she is made to bear children against her will, often in the context of slavery or extreme oppression.