Mama's internal narrative voice reveals her to be a great deal more perceptive than her daughter, Dee/Wangero, believes her to be based on her external, spoken voice. Her inner voice seems to work fast while her spoken voice is slow; her inner voice is detailed while her spoken voice is economical. For example, Dee and her new boyfriend (or husband -- we are never sure) seem to pass looks between one another, as if to indicate their shared judgment, and though Mama never acknowledges this aloud, she says internally, "Every once in a while he and Wangero sent eye signals over my head." Because she says so little of what she's actually thinking about and aware of, her daughter fails to realize how smart and perceptive Mama really is.
Something similar happens when Dee/Wangero insists on taking the quilts that had been promised to Maggie.
When I looked at her [...] something hit me in the top of my head and ran down to the soles of my feet. Just like when I'm in church and the spirit of God touches me and I get happy and shout. I did something I never done before: hugged Maggie to me, then dragged her on into the room, snatched the quilts out of Miss Wangero's hands and dumped them into Maggie's lap. Maggie just sat there on my bed with her mouth open.
When Mama speaks to Dee/Wangero, her sentences are short, efficient, and without judgment. However, when she speaks internally, she reveals herself to be quite discerning: referring to her daughter as "Miss Wangero" indicates a judgment of Dee's entitled behavior, and her description of her physical affection for Maggie shows her recognition of this daughter's limited expectations and hope. In short, Mama's internal voice is a great deal more perceptive and detailed than her speaking voice, which is much more economical and even deceptively simple.