Alba is one of the most important figures in the novel. In fact, we'd say she's a contender for the role of protagonist. This despite the fact that she's not even born until Chapter 9, over halfway through the book. But from the moment she pops her little green head out into the world, Alba is central to both the Trueba family dynamic and the plot. And to the novel's structure. And to most of the themes. See? We told you she's important.
When we realize in the Epilogue that Alba has been the fictional author of most of the book, the structure of the novel finally makes sense – we can see how her perspective, informed by Clara's notebooks that bear witness to life, colors the narrator's observations. Alba also brings about the story's resolution – it's her act of forgiveness towards her torturers that lets the novel end on a hopeful note. Alba opens up the possibility of a break in the pattern of violence that has hounded her family for generations.
Alba and her Grandmother Clara have an uncannily close relationship – so close, in fact, that Alba communicates with her grandmother's spirit even after her death. It's possible to read Alba as an extension of her grandmother's character, and this theory goes a long way in explaining Alba's sense of déjà vu upon writing her grandmother's story. Alba feels as if she's lived all this before, because Clara lived it (Epilogue.45).
The similarities between Clara and Alba range from the superficial – like good skin – to the symbolic. Alba mirrors many of the child Clara's actions when she's young, holding Esteban's hand, for example, when they attend Clara's funeral, just as Clara did when they attended Rosa's. She also imitates Clara's role as family scribe, beginning at a young age "to record the things that struck her as important, just as her Grandmother Clara had before her" (10.30). And the ability of both women to communicate across the divide between the spiritual world and the world of the living allows them both to act as spiritual mediators and guides, assisting in the transition between this world and the next. Alba, for example, helps Clara to die, while Clara comes back from the dead to convince Alba to live.
Both Alba and Clara fulfill a connecting role in the life of the Trueba family – in fact, they're the only two characters that maintain a relationship with all of the other family members. This is especially impressive with regards to Esteban Trueba, whose infamous temper and reactionary ideas isolate him from pretty much everyone else around him. Clara is, for a long time, the only person who can deflect his furious rages, and even after she symbolically divorces him she has a mysterious, pacifying effect on the old man. Alba, in her turn, is the recipient of all of Senator Trueba's "finest sentiments" (9.27). Other than Clara, Alba is the only person to ever show Esteban any tenderness, and she's the only reason he sticks around the house after Clara dies. Clara and Alba are the family glue.
Alba's arrest is the direct cause of Esteban Trueba's biggest breakdown – when she disappears, Esteban has lost everything, and reaches his lowest emotional point. Alba is therefore the catalyst for Esteban's redemption. Because of his love for her, Esteban is finally able to see that there's something more important to him than, well, himself. Alba, together with Clara's spirit, allows Esteban to die happily, at peace for perhaps the first time in his life.