Cecilia - Plot

I'm confused about her character. She shows up once early in the movie (the girl with the red and white checkered apron who says she has to work) and then once more at the end when Sandy is being committed to the hospital. I'm not sure what her purpose was but I'm thinking there's more to it.

I'm not sure if I understood the movie. I took it as Angela had multiple personalities. I remember something along the lines as Angela saying Sister Dolores told her she could have as many "friends" as possible, but Angela only wanted Sandy as a friend. While in her coma Angela created other personalities but wanted Sandy all to herself again and killed off her other "friends" until there was only Sandy left. I think once Angela's goal was achieved is the reason she awoke from her coma. I suppose it's possible why the black doctor/professor, Cecilia and others who end up at the hospital at the end, but were seen throughout the movie, are simply familiar faces from the hospital she's always been at.

I know it's a horrible explanation but any other comments would be insightful.