Sarah

Grandmother is a high ranking human at the Grace Field House, serving as its leader, who considers Isabella as one of her pawns.

When Krone told her about the escape plan of Emma, Norman, Ray, Don and Gilda, Grandma told Krone that she would leave it all in the hands of Isabella because she is important to her and above Krone in every aspect.

She serves the Demon Boss.

History
She was the one who found out how Isabella was climbing up the wall.