Do you have children already?
Maybe she would be willing to tell her children to their faces that “Base on my experience raising you, I don’t want any more children. I’m afraid they might turn out just like you.”
Sounds awful. But don’t candy coat a turd, you’re doing no one any favors. That is what contraception says to a child - you don’t want any more like them.
It’s sad. I’ve actually heard parents say similar stuff in the presence of their own children. One dad, when learning that he would be an uncle, exclaimed, “YES! More kids! And we don’t have to raise them!”
Of course he said it with a humorous tone - but I gotta believe he was revealing his inner thoughts on parenthood/children - they haven’t had any more kids.