Lacy is willing to use manipulation to get her mother alone. Her first line in the film is, “Hi, I’m gonna kill myself.” But Baker’s delicate spellbinders more often leave their themes unspoken. Her characters grapple with longings and a need to prove their worth, but they rarely share their struggles out loud. (The only time the script feels false is when Lacy claims that “every minute of my life is hell.”)

The one scene when Janet takes psychedelics, she fesses up to her harsh self-judgment only to be interrupted mid-breakthrough by her pal Regina (Sophie Okonedo). The conversation pivots to how irritating it is to be interrupted, and in frustration, Janet alludes to the several years Regina squandered in a sex commune under the thrall of a bearded cult leader (Elias Koteas) who boasts about his big crop of zucchini. Then, as the stoned women bicker, the top of Lacy’s head pokes into the shot and we realize Janet hasn’t cared that her daughter has been in the room witnessing the entire thing.

Baker’s style is commonly called realism or naturalism, yet slotting her into old-fashioned movements doesn’t feel right. “I feel like we lack any terms for playwriting that come after 1890,” she once said to the New Yorker. The stage directions for Baker’s plays (“Circle Mirror Transformation,” “Body Awareness,” “The Aliens”) insist on long pauses during which the audience watches her characters until it figures out what in the silence she wants it to see.

Now that Baker can point the camera where she wants, she and the cinematographer Maria von Hausswolff create images with the familiar graininess of a home movie and the intimate, askew angles of a glowering child. We’re in that back seat glaring at Janet’s latest boyfriend, Wayne (Will Patton) — a total drag. Planted here among these granola types, a new word for Baker’s work emerges: organic — the purity of capturing a setting so accurately that it roots the characters’ quiet beliefs.

Like the girl at the center of her film, Baker is a skeptical observer of a well-intentioned but disorderly home. From the “Free Tibet” bumper sticker to the bottle of henna shampoo, the details are so pointed that you feel absolutely sure that Baker herself was once a strange child exercising her need for control by way of a doll collection tucked into a makeshift stage, as Lacy does here. There are moments of recognizable precision — say, the sound of a grandfather clock chiming during a piano lesson — which trigger such a Proustian rush of pre-millennium adolescence that I had the eerie sensation that if I flipped through my family photo album, I’d see the top of Baker’s own head spying from the corner of the frame.

For a while, it’s easy to dismiss the film as simply a tone-perfect re-creation of that last era of analog youth when adults didn’t feel guilty for ranking their own needs above their bored children. Its soul emerges in the questions Baker waits for us to ask. What turns stubborn girls into pliable women? Was our personality forged in opposition to our parents, or will we repeat their mistakes?

Ziegler, a fantastic find making her own film debut, shoulders us through the story without ever getting too cute, while Nicholson’s turn as the vulnerable, optimistic Janet is calibrated to finely, finally elevate her from character actress to star. The leads contrast marvelously: lonely versus popular, closed-off versus permissive, the child cynic and the adult naif.

Eventually, the movie’s compass points us somewhere toward the middle, to mull not just what the mother can learn from her daughter, but whether the girl might decide it’s worth sacrificing a bit of autonomy to live a fuller life.

PG-13. At area theaters. Contains brief strong language and parental drug use. 113 minutes.