Why do you think Melinda feels as though her parents would be "divorced if she hadn't been born"?

What is the story or passage from the story that relates to what you're asking?

Edit: She thinks that Christmas needs little kids around to add to the festive spirit. Now, she feels that she and her parents are just going through the motions of celebrating the holiday and that her parents would be divorced if she hadn't been born.

Maybe she blames herself for her parents divorce