I asked Ms. Howe, who remains a close friend, if she’d ever regretted Ms. Bening’s defection to the movies. “Not for a minute,” she said. “I admire her for taking on Hollywood and for doing it on her own terms.”

In Los Angeles, where no one notices theater, she kept at it — Chekhov, Ibsen, Ruth Draper’s monologues. In 2014, she returned to New York, in a humdrum “King Lear” for Shakespeare in the Park. She entertained offers from Broadway, too. But when her children were at home she could never get the timing right — even limited runs didn’t coincide with school breaks. She always passed.

The children grew up. And last year the director Gregory Mosher offered her Kate in “All My Sons.” (After a dispute regarding color-conscious casting, Mr. Mosher left the production; Mr. O’Brien replaced him before rehearsals began.) She took it.

“All My Sons,” is a play about responsibility, corruption and the nexus, as Ms. Bening put it, “between a booming economy and bloodshed.” Joe Keller, Kate’s husband, owns a factory that manufactured faulty cylinder heads during World War II. Those cylinder heads were shipped to Australia and welded to bombers. Twenty-one pilots died. Three years later, in 1947, with one son returned from the war, and another designated missing in action, Joe has been exonerated, but the question of his guilt remains. “The play is asking, are we just responsible to ourselves or are we responsible to the greater good?” Ms. Bening said. “That’s a deep political question.”

But her relationship to the play, which she first saw as a graduate student, is more personal. And here at least, she wanted to talk. During World War II, she said, Russell Ashley, one of her mother’s older brothers, joined the Royal Canadian Air Force (he was too old for the American one) and deployed to India. “And he was killed because his plane had a mechanical failure,” she said. His body was never found. She has a photograph of her family shortly after. Her grandmother is 60 or 61 in the photo, the same age Ms. Bening is now. “There’s just this look on her face and there’s this —.” She let the rest of the sentence fall.

I asked what that meant for Kate and Ms. Bening evaded elegantly, describing unrelated sections of Miller’s autobiography, segueing somehow into “Who’s Afraid of Virginia Woolf?” (Several colleagues mentioned what Mr. O’Brien called “this unmistakable quality of intelligence.” Yes.) She acknowledged that her own experiences as a mother had informed the role, but only in the most general terms. “It would be psychologically, physiologically impossible to be an actor and not use anything about your own experience,” she said. (Using “you” and “your” rather than “I” and “mine” is big with her.)