| Quote #1
[Salander's] mother [Agneta] had spent ten years at Äppelviken, and it was where she finally died at only forty-six, after one last annihilating cerebral hemorrhage. (5.1)
At this point, we still don't know what happened to Salander's mother to put her in a nursing home so young and cause an early death. (She died in Tattoo.) This quote tells us that Agneta is only a few years older than Blomkvist when she died.
| Quote #2
As a teenager [Salander] had cherished the fantasy that her mother would get well and that they would be able to form some sort of relationship. (5.3)
We don't get Salander's memories of interacting with her mother before Zala beat her so badly that she suffered regular strokes. This thought make us really curious about those times. This quote also makes us see how much Salander's missed not having a mother in her life.
| Quote #3
She had no reason to love this apartment. She had moved in with her mother and sister when she was four. (7.37)
That means that the apartment Salander was living in all through Tattoo was where Agneta was brutalized by Zala and where Salander tried to kill him twice. It also means that where Mimmi was kidnapped is roughly the same spot where Salander set Zala on fire. Creepy.