This brought back nostalgic memories for the divorced witch, each time she'd birthed a baby... only for Lucious to send them away. It broke her heart each time since she'd had three daughters in the past before finally giving birth to Draco. He was supposed to be Lucius" heir... though bubbling in Narcissa's gut was despair and hatred for her husband. She couldn't overcome the loss of her three daughters. So Draco being impregnated was the last nail in the coffin for her. She'd lost all sense of rationality and only craved to make a new picturesque family from scratch... and she'd definitely achieve it too, starting with Harry.