Continuity mistake: In an early scene where the young Sally and Gillian are walking up to the aunts' house, the girls shown are the ones that play Sally's daughters and they're wearing velvet dresses. When they reach the aunts, the film shows the young girls that are actually playing young Sally and Gillian and they're wearing sailor type school girl uniforms.
Continuity mistake: Gilly is on the floor inside the circle formed by the other women to prevent her from escaping. Sally falls on her knees to be close to her sister. When the camera shows Gilly from Sally's position her head is turned right, when they are both in the shot Gilly's head is turned left.
Revealing mistake: When Sally and Gilly bury Gilly's boyfriend, you can see the "dead" body breathing heavily while it's raining on him.
Continuity mistake: Where did Sally get the bottle of rum since Gillian broke it in the sink in an early scene in margarita time? Same bottle with the same amount of rum in it.
Continuity mistake: When Sally is talking to Gillian after the first failed exorcism attempt, we see Sarah is wearing white shoes; but when they are pouring the potion on the grave, she has brown sandals.
Continuity mistake: Hallet takes his jacket off twice when he's in his room with Sally.
Answer: She is the one from the opening sequence, their "great, great, great" grandmother who started the whole "curse" thing.
Bruce Minnick