Loyalty and forgiveness
Instead of developing a deep hatred toward her father for the life he stole from her in his violence and anger, Marina learns the power of forgiveness, and even if her decision is naïve to return to her abuser, the decision is also a powerful indication of Marina's moral integrity and loyalty.
The value of company
Even though she can't overcome her aversion to speaking, Marina learns to make friends through non-verbal communication. It seems the invitation to play, fun, and learning are simply too powerful for her to resist, and perhaps this participation leads her to her breakthrough.
The innocence of a child
By focusing the readers attention on the daughter instead of the parents, the novelist highlights the true tragedy of children suffering before they are old enough to understand why bad things happen (not that people really ever figure that out, but for a child, it's particularly regrettable). In the end, it's her child-like resilience and love that guides Marina out of her post-traumatic episode.
