Acting in films under two female directors, Rebecca Miller and Mia Hansen-Love, helped “shift” something in her. She recalls a conversation with Hansen-Love, who had been in two films directed by her partner, Olivier Assayas. “She had worked at Cahiers du Cinéma,” Gerwig says. “She said that the other young male writers there treated her dismissively because they thought of her as Olivier’s girlfriend, who got there because she was his girlfriend, and how they changed when she had her first movie at Cannes, when she was in her 20s. All of a sudden they looked at her like they’d never seen her before. I hung onto that story. All those little pieces I put in my pocket. I think I needed these little signs.”

Several years ago, Gerwig was at Miranda July’s house. It was early in their friendship (and before Gerwig’s turn as a punk photographer in “20th Century Women,” which was directed by Mike Mills, July’s husband). On her way out, July offered her a pair of shoes: Rachel Comey loafers that didn’t quite suit July. Not long after, Rebecca Miller, who was directing her in the romantic comedy “Maggie’s Plan,” handed over a pair of “sturdy English shoes that you can see women wearing who were on their way to work in the ’30s.” The meaning wasn’t lost on Gerwig. “I thought, If I wrote this into a movie, people would think it was too obvious of a symbol,” she says. “I was literally given shoes by two female directors. And it felt like, if you’re looking for a sign, there you go!” The shoes acquired talismanic powers. She wore them to the “Lady Bird” set whenever she needed an extra boost.

Movie sets have not historically been comfortable environments for women. Less than a month has passed since the publication of the articles in The New York Times and The New Yorker claiming sexual abuse of women by the Hollywood producer Harvey Weinstein. That Gerwig is a confident young woman making movies about confident young women feels especially meaningful right now. It is not merely Gerwig’s being a woman that feels relevant but her directorial style. She extends the same protective impulse to her cast that she does to her characters, saying that the job of a director is to “hold the perimeter” of “a bubble of magic safety” so that actors can play. I spoke with several actors from “Lady Bird,” as well as with Sam Levy, the cinematographer, and heard again and again how cared-for, and safe, they felt on Gerwig’s set. She ran rehearsals at her apartment and conscripted the cast into awkward dance parties (a trick cribbed from Mills). She encouraged the actors to have secrets from her — things they knew about their characters that she didn’t.

“I trusted her completely,” says Metcalf, who adds that she relied on Gerwig to help her understand the character of Marion. “On the page it could just be like a nonstop aggression. But she taught me what the character was covering up.”

“I wanted Marion to secretly be the main character,” Gerwig told me. “I kind of wanted her to take over the movie.”

The history of mothers on film is one littered with angels and witches. Marion is neither. She’s tender and loving but doesn’t know how to express it; she is often impatient, can be nasty and aggressive and doesn’t support Lady Bird in the way she wants to be supported. (We might call this good mothering, in that she is helping Lady Bird to separate from home.) She doesn’t exactly take over the movie — the film ends on a shot of Lady Bird, alone, on a New York street, with Marion left behind — but she does center it. There is one scene in particular that is a kind of anchor. It shows Marion at her sewing machine, fixing a dress that Lady Bird will wear to a fancy Thanksgiving dinner at her boyfriend’s grandmother’s mansion. Marion would prefer that Lady Bird spend Thanksgiving at home, but she’s helping her anyway, first by shopping with her at the thrift store, and now by mending the dress.

The shot is framed squarely, in dim lighting, with Metcalf looking drab and dour in the center. It is very brief, a few seconds long, and silent, except for the wild thrum of the needle. It’s Gerwig’s homage to “Jeanne Dielman, 23 Quai du Commerce, 1080 Bruxelles,” Chantal Akerman’s classic 1975 drama of a three-day unraveling, consisting mostly of shots of a woman doing repeated household chores. Gerwig told the audience at the New York Film Festival that she was moved by a remark that Akerman once made about the importance of seeing images of housework on film. “We value watching a woman get raped more than we value her making dinner,” Gerwig said, incredulity and disgust mixing in her voice. If there are Lady Birds in the world, it is only because there are Marions — mothers, and foremothers — who brought them up. Lady Bird will put on the dress and wear it out and think nothing of it. But we saw the care Marion took, late at night and all alone, to alter, ever so slightly, what was possible.