If encountering her after Ethel is dead, she is no longer hostile, but her sanity not intact anymore. She is still hostile if Ethel has been defeated but the party accepted the offer of Hag's Hair and let Ethel escape.
Combat
Attacks and abilities
Mask of Servitude must succeed a DC 17 Wisdomsaving throw at the start of each of her turns or become affected by Hag's Pawn. If she succeeds the throw, she passes the turn without harming the party.
Mask of Servitude acts as a healer and buffer for Auntie Ethel and the other Masks.