Actress Penelope Mitchell arrives at the TCL Chinese Theatre for the premiere of Netflix’s “Arrested Development” Season 4 held on April 29, 2013 in Hollywood, California. (Jason Merritt/GETTY IMAGES)

Although she walked at 7 months old, actress Penelope Mitchell never was a child. She’s making up for it now. The co-star of the Netflix thriller series “Hemlock Grove” started studying ballet when she was 4, and for 12 years she applied her considerable determination to the art.

“When I was 16 I said, ‘All right, now I need to stop all this nonsense and focus on my academics.’ So I spent two years with my head in the books,” she says in the courtyard of a hotel in Pasadena, Calif.

“I stopped drama, everything, and I became incredibly depressed. I was so sad and I didn’t know — I thought that was just a given. ‘Yeah, I’m stressed. I’m working hard, of course I’m depressed.’ It was actually because I wasn’t breathing and I wasn’t feeling anymore,” says the slender Australian, who mastered an American accent for her role as the fragile Letha Godfrey in “Hemlock Grove.”

“My first year of university I ran around and signed up for these clubs and I noticed they were all drama clubs, really lame, artsy things,” she giggles. “I was looking over my shoulder to see if anyone was looking at me.

“At the end of my first year, I realized I wanted to do more drama, so I actually started an extracurricular course outside of university. So I was at school all day writing and in the evenings I’d go to drama school. So it was nonstop.”

For most of her life Mitchell, 23, did everything with obsessive dedication. She modeled for two years when she was 15 but buckled under the pressure. It was about that time her father suffered some financial reverses and could no longer afford to send her to a private school in Melbourne.

“I had a lot of gumption and I was very forthright and made a plea to the school to keep me there under the proviso that I’d work super, super hard and pay whatever was left with my own funds,” says Mitchell, who’s dressed in a plaid wool jacket, navy top and charcoal capris.

“So I took out a loan and paid for the semester. . . . High school for me was a blur because I was so manic. It was nonstop. I ended up in the top percentile of my state, which is how I got into the university I got into. I was nuts. I’m still nuts,” she smiles.

Her dad is an entrepreneur and her mom a French-born artist with a variety of talents. When Penelope was 5, her mom took her and her two older brothers to France to live.

“I remember being this little girl missing her daddy and living so far away in France and from anything that was familiar to me. I felt so different and so isolated. When you’re removed from everything that’s familiar, you realize who you are.”

Returning was equally traumatic. “When I came home after that I was never quite the same person, and going through school after that I never felt like I belonged there either,” she says.

“And I always felt like an outsider and always felt like an observer. Even though I was manically overachieving and involved in everything, I still never felt like I belonged. That’s definitely affected my whole life and why I wanted to become an actor and tell people stories, because communication and feeling like you belong is such an integral part of our social fabric.”

After college, Mitchell headed for L.A. Her actress cousin, Radha Mitchell, lived there, though she was out of the country. For the first two months, Penelope stayed with friends.

“I was running out of money very quickly and I knew I had to get something. I got sent this audition [for ‘Hemlock Grove’] on a Thursday night and . . . my agent said, ‘Drop everything. I want you to read this.’ I picked up the script and it was weird. my last year of college all the subjects I did were Gothic literature. I was fascinated by it. When I started, I loved Keats and all the romantics — perhaps it was because I was a ballerina and I was very naive. At the end of school, it was all about Byron, about dark men. When I got the script, I thought, ‘This is amazing.’ It was all of my favorite books in one script.”

She tested on Monday. Two days later, she had the part. “I’m very big on instincts, intuition and fortuities and serendipity. And I just knew that was where I was supposed to be,” she says.

While all her practical endeavors paid off, she remarks, “I only failed at life. I knew what I wanted. I modeled to pay for school and worked super hard to be in school and to get to university. I always had my eye on a prize. As a consequence of that, I was perpetually living two steps ahead and was never present. And that does terrible things to one’s body, psyche, soul, general well-being.

“I was pretty miserable. I was hugely masochistic, and to me it was just a means to an end. It wasn’t till I graduated from university that I fully respected myself and decided I wanted to pursue acting. And I felt happy for the first time in my life. It’s pretty huge.”

— MCT Information Services

Hemlock Grove

Available for streaming on Netflix.