"Voldemort knew of the Compulsion-based Bonding that essentially made these two women magically married, and in his hope to have a new generation of competent Half-Blooded Death Eaters, tasked them to reproduce by use of a modified polyjuice potion. He even marked Hermione with a curse, as you can see on her right wrist, to force her to be loyal to him else he track her down and make her suffer a slow and painful death. She was as dammed as any other Death Eater was, except that she never chose to take the mark of her own free will.