My theory is
What happen to Rood can very well be what happen to Meredith.
What happen, you might ask?
Remember Mikel experiment on Rood during Master's day as tower magician? Rood Is the only child to successfully set foot on demon world and bound with the dk.
What if the same could have happen long ago, whereby meredith is the only survivor and dk bro is the one that bound with Meredith