[Spoiler alert: The following interview discusses plot points from the entire fourth season of “Orange Is the New Black.” Do not read until you’ve watched.]

Lori Petty’s Lolly Whitehill is such a central part of “Orange Is the New Black” season 4, that it’s easy to forget she hasn’t been there all along.

After a brief guest turn in the second season premiere (when Piper was on the plane to Chicago), Lolly returned last season to spook Alex (Laura Prepon), who thought she was sent to kill her. As it turned out Lolly was simply following the voices in her head — a paranoid schizophrenic, Lolly is convinced all government agencies are united in a conspiracy to kill her.

This season, Lolly saves Alex’s life by knocking out the prison guard who turned out to be an undercover assassin, helps Alex bury the body, and later bonds with Healy (Michael J. Harney), who convinces her that it was all in her head. Sadly, it wasn’t, and when the truth is revealed Healy is forced to escort Lolly to psychiatric prison in one of the season’s most harrowing scenes.

Joining “Orange” has reenergized the veteran actress. “It’s been so much fun in act four of my life to be attacked by 10-year-olds wanting selfies, it’s just hysterical,” Petty says. “It’s so funny, to be part of a cultural touchstone right now. I’m really thankful.”

She spoke with Variety about how she joined the show, finding the humor in Lolly’s eccentric behavior, and whether or not “Orange” fans will see her again.

Lolly was only in the premiere of season two and then eight episodes of both season three and four. Was it always the plan to gradually make her a more important part of the show?

What happened was, I saw the show [in season one] and I was like, “Why am I not on this show?” I joined SAG in 1985. I’ve learned a closed mouth doesn’t get fed, you have to ask for what you want. I saw the show and was like, “What the hell?”

I was in New York at the time at Blue Ribbon, a great restaurant, and I went on IMDb to look up the casting office and it was across the street from Blue Ribbon. Seriously. I called my manager and said, “I need you to call Jen Euston and tell her I’m downstairs.” She said, “You want me to call the woman who cast ‘Girls’ and ‘Orange’ and tell her you’re downstairs?” I said, “Yes!” So she called her and Jen was like, “Yeah, f— yeah, send her up!” These people are in their 30s, they grew up watching “League of Their Own,” “Point Break” and “Tank Girl.” Even if she doesn’t want me on the show, she’ll be curious to find out what the hell Lori Petty wants. I went upstairs and we talked, a couple months later they called and said, “We have this part.”

I went and did that scene on the airplane [for season two]. Jodie Foster directed it. We were halfway through the day and I was like, “Why haven’t these people asked me to become a regular yet? It’s lunchtime, what’s up?” I went to a producer and said, “I’d like to come back, what’s going on?” They said, “We shot out of order.” They shot the first episode last that season. I couldn’t come back until the next year.

And how much did Lolly change when you returned in season three? Looking back at that season two episode it doesn’t seem like they’d quite figured her out yet.

They hadn’t, it wasn’t all fleshed out. What they’re really good at is, they’ll write an episode and then they watch and see what you do with it, and then they move in that direction. It’s a really cool dance, how they play into your strengths and surprise the s— out of you. Every week it’s like they learn more and we learn more, we learn together. It’s not all planned out, like “you’re Thomas Jefferson.” It evolves.

Did you know at the start of season four how deeply they would get into Lolly? Or did you just get the first script and see she’d kill somebody?

Yeah, that’s really it. It’s a new business plan. Netflix is a whole other animal. If you’re on ABC they’re gonna say, “here’s your five year contract,” or “you’re gonna be in 13 episodes.” It’s a whole other business model where they say, “Do you want to be on the show this week?” and I’d say, “Yeah.” I had no idea what was coming.

Was there a certain point when you realized how much she would grow this season?

I think even episode one when I came in and saved Alex — just our Abbott and Costello, straight man-funny man gig, it threw all of us — me, Laura [Prepon], everyone — off guard. We just went, “How is this so funny and so horrible?” [Laura and I] work really well together. That was a welcome development. It was this new cool happening, the kinetic energy between us. They gave us more to do together and it just worked so well. The characters are so different but they understand each other.

The season gets so dark near the end but the early episodes are really funny, even though you’re dealing with a dead body.

Seriously, my favorite line of the whole season is my first line. The whole season is brilliant, but when she kills a guy and says, “So, there’s this big hole in the fence and everyone’s going swimming, I just thought maybe you’d want to go.” What the hell was that? It was so awesome. Just them allowing me to be silly in the midst of murder was a real gift.

What did you think when you read episode seven and the flashbacks to Lolly’s past?

They kept telling me, “Episode seven is coming!” I was like, “Okay, I’ll read it when I read it.” But it was fantastic. It shows the truth. Crazy people get locked up now, there’s no mental health government subsidized places that take care of people. I live in Venice Beach and I see these poor homeless people obviously in need of medical attention and they’re just homeless, that happens. Usually the cops turn a blind eye because they don’t want to deal with all the paperwork and figure out where to take you and “How crazy are you?” They usually just look away. Or you get locked up. As it stands, [Lolly] didn’t really do anything wrong, until she got to prison. She was in need of help and nobody helped her.

Christina Brucato does an uncanny impression of you as young Lolly in that episode.

People thought it was my voice, they thought I was there. She was really exceptional. We worked on different days, I never worked on a day she worked. We weren’t ever together because we’re playing the same person. She just studied and watched, it was all her. I came in to get my hair bleached one day and saw her getting her wig done and said hi, that was it. That was all her. I didn’t help her at all.

So it wasn’t until you saw the episode that you saw what she did?

Yeah. I heard how great she was, people told me when I went to work. They said, “We thought you were there. You’re gonna be blown away how good she is.”

Lolly’s final episode of the season, episode 11, is a real heartbreaker. How did you feel when you read that?

It was horrific. I’m so blessed to have Michael Harney as a partner, he’s just the best. We could trust each other and do our work. I’ve learned so much from him on every level. He’s just fantastic. To have someone who has your back, who’s not gonna let you go is imperative. When they took me down the hall [in the psychiatric prison] — they didn’t show on the show what was there, they had some awful things that were so awful I think they just cut it out. The stuff I was looking at was just beyond. I didn’t want to look at it until we were filming. What you see is real. I guess it was more powerful to watch me seeing it than to actually see it. There were people tied down, people caged up, people being medicated. It was just awful.

Your reaction is very powerful — was that all from what they had there for you to see?

I guess it’s Method, but if you tell me, “You just got run over by a train,” I’m like, “Okay, action! Ow!” You believe what you’re doing. That’s all acting is, it’s actually believing it. Imagine that happening to you, that’s pretty easy to do. It was rough on everybody — the crew, everyone — it was really torture. And that’s what they do to people. I had a shrink once — I don’t go to a shrink now, but I did a long time ago — he said, “People think when people get sentenced to psychiatric prison that they’re getting off? Oh no, you want to go to real prison. You don’t want to go to psychiatric prison. That’s just inhuman.”

Did you do any research into those facilities or mental illness? Lolly’s illness isn’t really specified.

I don’t know why, but I’ve played a few characters with mental illness so I’ve done research before. I’ve been to USC and learned about different disorders. When I did “House,” the character had a terrible Huntington’s disease, I learned a lot about that. I’ve done research in the past. With Lolly, it’s schizophrenia. She has a really good heart, she’s trying really hard to do her best, but the voices… She’s smart enough to know they’re not real, but like she says, “It doesn’t mean they don’t have something to say.” They’re still talking. She’s trying to deal with it the best she can, she just hasn’t been helped. I think that’s why she tries to help other people, because a lot of times you give what you really need to get.

I asked Uzo Aduba about this too: Both Lolly and Crazy Eyes are very funny characters, but how do you balance that humor without making it feel like you’re joking about mental illness?

You can’t be funny unless you’re smart. Crazy Eyes and Lolly are both very intelligent people, we’re just not on the same wavelength as other people. It’s not like we’re dumb and you’re laughing at us. That s—’s funny, it’s funny because it’s funny. I was with Eddie Murphy once and we were watching Mo’Nique, I couldn’t stop laughing. I was dying laughing. I looked at Eddie and he was really serious watching the TV, and I said “Why is it so funny?” He said [in a serious voice], “It’s funny because it’s freaking funny.” He was studying it. That’s the thing, you have to be really smart to be that funny. To be Eddie Murphy, to be Uzo, to be Mo’Nique, they’re smart. Same with Lolly, she’s smart, she’s not stupid. And I like comedy, I can’t help it. I’ll read something and I’ll perform it and they’ll go, “No, Lori, it’s not supposed to be funny.” I’m like, “Oh, s—, sorry. My bad, I’ll be serious.”

It’s almost selling her short to say she can’t be funny or have a sense of humor. It’s a small thing, but I love when she’s walking by the restaurant right before she’s arrested and says, “Ooh, green spaghetti, what are they gonna think of next?”

That was an ad lib. I was in character, I was just supposed to say something about gentrification, but I still have however many feet to go to get to where the cops are. I had to fill the space, so I came up with that. They’re good with that at “Orange,” Taryn [Manning, who plays Pennsatucky] does that a lot too. Taryn is so damn smart. She’ll basically say what they wrote [laughs], but her character is on her own trip. The people who are on their own trips, it’s hard to be completely true to the lines all the time. You’re out there, actually doing it.

Lolly isn’t in the final two episodes, but did you get the scripts? And when did you find out about what would happen to Poussey?

They sent me the scripts. I found out when everyone else did. I know Samira [Wiley] knew forever. I talked to her, everybody talked to her. It blew my mind. She’s a star. You don’t kill Brad Pitt. You don’t kill George Clooney, you know? I directed a movie called “The Poker House” and cast Jennifer Lawrence in her first role. When I saw her tape, I just had to cast her. It’s the same with Samira — I saw her and it’s like, “Goddamn she’s a movie star.” She’s just got it, she holds that screen. I’m proud of her. It was devastating, and Danielle [Brooks] really brought it home.

I know nobody knows much about season 5 yet, but have they made any overtures to you coming back? I hope that’s not the last we’ve seen of Lolly.

They’re still writing. I don’t know what’s up. They’ve got 100 characters to deal with. It’d be my extreme joy to be back. I’m hoping that happens. They haven’t started shooting yet, so I don’t know.