She was wrong on a lot of counts. First, you can’t pick your family. Second, why talk politics to children who can’t vote? Third, she is wishing death on this kid because someone living in his house disagrees with her politics. I know that if this kid or any part of his family dies, this woman would be ecstatic. It’s amazing how one person’s ignorance can be so harmful much less millions.
Even in the heat of the moment, unless the conservative kid had wished her dead (quite unlikely) there isn’t any way to explain why she’d say something like that other than that she was badly, badly wrong.