To Jennet, revenge is a dish best served cold... or hot, or on the side, or fried up in a tasty hash, or pretty much any way she can get it. What we're saying is that this chick likes revenge. Even though her son Nathaniel's death was no one's fault, she's super cheesed at the injustices that have been piled on her. But she's not content to stew in her own hatred. In death, she takes it out on other people's children—and in a final, heartbreaking twist, on Arthur as well. But will that be enough for her?
Jennet is taking revenge on the community that would not allow her to raise her own son.
In taking revenge on Arthur, the woman in black brings resolution to the whole story... even if it's kind of bleak.