ADVISORY: This story contains mild spoilers for HBO’s Mare of Easttown.

Ariel Stern knew how Mare of Easttown would end long before the HBO drama wrapped up its seven-episode run on Sunday with Kate Winslet’s Mare Sheehan climbing up to the attic of her home, the spot where her son Kevin had died of suicide.

Stern, a therapist and the clinical director for the Ardmore office of A Better Life Therapy, was a consultant on the show, a murder mystery that also proved to be a meditation on grief, with Winslet portraying a police detective who used her work to avoid dealing with the pain of losing her son.

“A big thing we talked about was [Mare] going back up into the attic at the end,” said Stern, who spoke with Winslet and Brad Ingelsby, the drama’s Berwyn-raised creator, before filming began, and was present for Winslet’s scenes with Eisa Davis, who played Mare’s therapist, Gayle Graham.

» READ MORE: ‘Bravo!’: Readers weigh in on the ‘Mare of Easttown’ finale

“That was something that they were really interested in: How can we visually depict that she’s had a healing moment? And how do we make that authentic, and not sort of cliché? … Would she have avoided that part of the house? And then could she go back up there in the end?” said Stern in an interview last week.

“That was a really important scene, because … they wanted to show that people can heal and that people can get better.”

As for the therapy scenes between Winslet and Davis, “I thought they were really excellent. I mean, I think it’s really hard to depict therapy in just a couple of short minutes, because ideally, it’s a long-standing relationship,” Stern said.

“They showed that there was sort of a linear build of the relationship between Mare and her therapist, that she got more comfortable, that she went back, voluntarily [after her mandated therapy was over], [and] they touched on the idea that mandated treatment can be a different ball of wax” from treatment that’s voluntary.

» READ MORE: Kate Winslet on HBO’s ‘Mare of Easttown’ and that Delco accent: ‘I’m an actor who doesn’t like to get things wrong’

“I’m biased because I was part of it. But I thought that the way that they wrote the script, the therapist asked some really good questions,” said Stern, who also praised Davis’ performance.

“I had lunch with her the days that I was on set, and I was like, ‘Oh, you’d be a really good therapist. You know, you’re very warm and open and friendly.’ ”

» READ MORE: What did you think of that ‘Mare of Easttown’ finale? Tell us here.

Being present for some of the filming gave Stern some appreciation for all that goes into making a TV show or movie. “I feel like I’m gonna watch the Oscars differently now because I’m like, wow, people really do care about sound editing.”

But reading parts of the scripts, getting “some spoilers” from Ingelsby, and spending time on the set didn’t hurt her experience as a viewer, said Stern, who thought the whodunit component of Mare of Easttown could have ended in other ways and still have been satisfying.

“I thought that the whole series was so suspenseful that I kind of gave up trying to figure out what happened. Even though I kind of knew.”