Continuity mistake: In one scene with Dahlia and Ceci sleeping in the same bed, Dahlia is awoken from a bad dream. The kid rolls over and pulls the blankets over her shoulder. The next shot, from the hole in the ceiling, shows the blankets around her waist.
Factual error: When Dahlia is on her cell phone with her lawyer, she goes down into an underground subway and is still talking to him. Her call should have been cut short, because cell phones in NYC don't work in underground subways.
Continuity mistake: In the scene when Ceci's father drops her off to the apartment for the first time, she jumps out of the car with her new Barbie. She runs to her mom with it in her left hand, then swithches it to her right hand before her mother picks her up. But in the next shot the doll is back in her left hand.
Continuity mistake: At the end of the movie when Kyle and Ceci drive up, Kyle's car is dirty, when they leave, it is clean.
Answer: The drunk woman in the begining of the movie was Dahlia's mother. (Remember, the husband was going to say that Dahlia was unstable because she had an abusive father and an alcoholic mother) That was a flashback. Dahlia was dreaming when she saw herself throwing up in the toilet.