The Old Ones can't bring back Mrs Devril because she fell into a tank of radioactive acid. She would have been totally destroyed I'm not sure if any of her atoms survived. Unless the Old Ones what to bring back a big space of NOTHING Mrs Devril will not come back.
P.S Have you noticed that Devril is only one letter away from DEVIL
That would be true if Mrs Deverill's name was spelt like that. It's not, her name is Mrs Deverill.
(Soz, I'm not picking on you or anything)