Ms. Caruso talks every script over with her parents and her mother researches “every single person that’s involved to make sure that she is safe,” Deena Caruso said. Ms. Caruso’s parents know that their daughter is drawn to what Deena Caruso calls, “things that are just edgy.” They go to the edge with her, walking her home from the stage door after.

“Beetlejuice” is the first show she has rehearsed away from her parents. “Last night was the first night that she’s ever been alone,” Deena Caruso said. “She’s in D.C. on her own.” She sounded as though she were crying.

I had worried, maybe unfairly, about that never-had-a-childhood stuff. But Ms. Caruso said that childhood never interested her. “I just never got along with kids my age,” she said. “I just didn’t relate.”

Her colleagues and family describe a preternaturally poised and diligent performer. Both Ms. Kauffman, “The Nether” director, and Alex Brightman, who stars with her in “Beetlejuice” and who’d supplied the temporary tattoo she wore that morning (“a watercolor of a flower situation,” Ms. Caruso said), used the exact same phrase to describe her: “more mature than any of us.” Condescend at your own risk.

Every so often Ms. Caruso wonders if she’ll wake up at 98 with regrets, but she doesn’t think so. I asked her, mostly joking, if she’d miss never having gone to prom — I guess I was thinking of “Pretty in Pink” — and she looked at me with high disdain and said, “That kind of thing — I just — no.”

Does she go out with friends? Not really. What does she do for fun? She reads. She watches old movies. She plays with her dog. She bakes. She’d prepared treats for the cast that morning, vegan and gluten free. (At this point, her personal press representative, who had been hovering in a corner, broke in to assure me that Ms. Caruso did have age-appropriate friends, that she did have fun.)