What is the importance of the birds in Chapter 28 of the novel, We Are Okay?

In Chapter 28, the bird that appears symbolizes the freedom that Marin lacks, for her wings are clipped. Marin sees a bird “come and go” outside her window before thinking that she “should have gone with [Mabel]” (213). Mabel regrets not having the courage to fly away with Mabel to California and adopt the Valenzuela family as her own. Marin perceives her life as out of her own control; she imagines a lack of self-agency.