Companion
Character Role Analysis
Turtle
Turtle falls short of being a full protagonist of The Bean Trees because she isn't a fully independent and fully-realized character. Which is pretty normal, for an infant (even though Turtle's not the most normal as far as infants go).
Although she does talk a little bit by the end of the novel, Turtle stays mostly mum throughout the bulk of it. She's a toddler, after all, and one dealing with serious emotional trauma at that.
More than anything, Turtle's role in the novel is to be a companion to Taylor. Because of her, Taylor steps into a new role as mother/single parent—a role that makes her "come of age" in a whole new way. When it comes right down to it, Turtle is little more than a supporting character in the Taylor Greer show, but don't worry: when she appears again in the novel's sequel, Pigs in Heaven, she gets a much more complex part to play.
Lou Ann Ruiz
Although two early chapters of the novel are devoted to Lou Ann Ruiz rather than to Taylor Greer, like Turtle, Lou Ann is really a supporting character in the Taylor Greer show. The two chapters that focus on her story serve primarily to set us up for the moment that she and Taylor finally meet.
Throughout The Bean Trees, Lou Ann is always represented through Taylor's perspective, and although the two young women are close, Taylor thinks of her as one close friend among many.