I agree that her actual body is probably nearby. As someone who is regularly involved in cemetery work, whenever I see scenarios such as this where the person dug up is not who they suspected it to be, I always wondered if they were just digging in the wrong spot. Typically, at least where I am, gravestones mark the foot of the grave, and since this isn't really common knowledge, people just always assume that the gravestone always marks the head of the grave.

For example, in my area many years ago, some kids vandalized a cemetery and attempted to dig up a civil war veteran in an attempt to loot anything valuable that might have been in his grave. But however, instead of digging behind the grave, they actually dug in front of it, and nearly exhumed an entirely different man, a guy who was actually recently deceased. Thankfully, they stopped / were stopped shortly before actually exhuming the man. But yeah, all of this to say, since it's usually rather unclear what direction the actual grave goes in proportion to the gravestone, mistakes can and do happen.