Ms. Lange’s absorption in the visual, her medium and herself, is sometimes painfully evident in “Dorothea Lange: Grab a Hunk of Lightning,” which, as directed by her granddaughter Dyanna Taylor, defies our usual expectations about the documentary-by-relative: Ms. Lange, whose images did much to define the Great Depression for mainstream America, was far from a perfect person, or mother. And Ms. Taylor does little to disguise the fact.