She wasn't normal to begin with. How long had she lived in that village with the zombies, not aging at all? A hundred years or something, it was. So, she wasn't exactly a regular human who would turn into a zombie like anybody else, I'd guess. Perhaps her body died now, but otherwise nothing much changed.
I just threw lich there because it's an undead generally not with a perfect human body but with the full mental faculties, and oft enough in charge of lesser undead. Not to mention becoming one is apparently the goal of many necromancers.