Cara Buono‘s daughter has grown up on the Stranger Things set — and she’s picked up a thing or two from the Duffer Brothers.

Buono, 54, has played Karen Wheeler, mom to Nancy (Natalia Dyer), Mike (Finn Wolfhard) and Holly (Nell Fisher) since season 1 of the hit Netflix series, and has been bringing her daughter Esmé along for the ride ever since. Now 13, Esmé has grown up alongside the cast — namely Wolfhard, Millie Bobby Brown, Noah Schnapp, Gaten Matarazzo and Caleb McLaughlin, who were all between 11 and 13 when they were cast — and Buono tells PEOPLE that she has some ideas about the show.

“My daughter has been coming to set since she was 3, and she always had really interesting theories about things that were happening on set,” Buono says.

“In season 4, at the end, when there are all those little white pieces of what looks like snow coming down from the sky, she had said to the Duffers that she thought that they were bits of bone from the various people who were killed in the Upside Down,” the actress recalls. “This was at age 10.”

“They’re like, whoa,” she says of how Ross and Matt Duffer, who created the series together, responded to that theory.

“She wants to be a writer,” Buono continues of her daughter. “So she’s just honing her skills now — her imagination.”

Esmé didn’t exactly make it into the writers’ room before the show’s fifth and final season, but she did get to be on camera for the first time in the show’s latest installment.

“She got to do a little background work, and it was really fun because she tried on some of my wigs, and there was one day actually where we were both working in different scenes, and it was really surreal to both be in the ’80s looks together on set,” Buono says. “[It was] really special.”

On top of bringing her daughter to visit the set frequently over the show’s nine years of filming in Atlanta, Buono says she was the “de facto mom on set,” particularly in the show’s early days.

“All of the young actors have been extraordinary,” she says. “I really, truly love all of them. And I’m excited to watch them all continue on in their incredible journey in their lives.”

“I’m very nostalgic,” she continues. “My daughter is 13, and I look at her, and I often think I see the 3-year-old. I see the little girl, and I think, ‘Where did she go?’ And it’s similar to that [with the younger cast]. I’ll look up at Finn, and he’s so much taller than me, and when we started, he was up to my elbow.”

She adds, “It’s very special, in that regard, to have known them when they were so young and [to have] watched them grow up and have that connection.”

While Buono is keen to share her daughter’s theory about the Upside Down, she’s tight-lipped when it comes to another major fan theory about Karen — and her possible connection to Vecna (Jamie Campbell Bower).

When asked about speculation that there could be a connection between her character and the show’s main antagonist, the ruler of the Upside Down and former Hawkins resident Henry Creel, Buono says only: “I have been told about the Karen-Vecna theory.”

Volume 1 of Stranger Things season 5 is now streaming on Netflix. Volume 2 drops Dec. 25, followed by the finale on Dec. 31.