If you find it hard to believe there's anyone in Los Angeles who hasn't heard of Kristen Stewart, you can't have met Errol. The octogenarian manning the local polling station for Democratic nominees is oblivious to the megastar standing in front of him. 'And you are?' he demands while flicking officiously through his register. 'It's S-T-E-W-A-R-T,' Kristen whispers, not wanting to loudly proclaim her full name, which must seem like it belongs more to other people than it does herself.

But nope, Errol does not quite hear her so she reluctantly inches up the volume to announce herself once more. Then there's a problem – it's the first time Kristen has ever voted ('It's terrible, I know, but I've always been away or in this weird bubble') and she's been marked as an absentee. Errol does not approve and gives her a form to fill in. I reckon she's quite enjoying this entirely normal interaction – the form not being whisked away and sorted out on her behalf must be a novelty. She pulls out a driver's licence, which features a photo of a girl who looks a lot like Twilight's Bella Swan, and gets to work. Once her vote has been cast,for Bernie Sanders by the way, we both get an 'I voted' sticker and I feel proud to have done my bit for US politics – even if as we're driving back to her home in a nearby gated community, it's announced on Twitter that Hillary Clinton has pretty much won the Democratic nomination.

She drives like she talks, veering off fast in one direction then stopping abruptly before jolting forward again. Hunched over the wheel swearing like a trooper, Kristen is a compelling combination of edgy and a Kerouac kind of cool. She's 26, the same age as my younger cousin (to whom I'm very close), and I find myself slipping into the same role I have with her: protective yet practical, keen to make things comfortable for someone who is slightly less socially confident than me. She won't do up her seatbelt, despite the car's incessant beeping and in the end I tell her to buckle up for goodness sake, and she does. I feel instinctively that I want to keep her safe. There's a withered red rose on the dashboard and I have a hunch who it's from (stay tuned). The fact that she keeps it there makes me think my instincts might be right – she's one of those people who cares so acutely they're forever teetering on the edge of suffering. But then, as Anne Brontë wrote, 'who dares not grasp the thorn, should never crave the rose.'

Later Kristen tells me, 'There are some people who are really consumed by their relationships, and some who compartmentalise and focus on other things. There are just some people in life who f*cking feel so much and some who don't let themselves go there.'

'So are you the former?' I ask. 'Yes! I think also right now I'm just really in love with my girlfriend. We've broken up a couple of times and gotten back together, and this time I was like, "Finally, I can feel again".' Her girlfriend is Alicia Cargile, a digital effects artist. She is not, nor has she ever been, Kristen's personal assistant. ('It makes Alicia so mad when people write that. She's a really successful artist in her own right.')

Kristen Stewart Liz Collins

Kristen Stewart Liz Collins

We're back at her home in the suburbs of LA's bohemian Los Feliz district, drinking iced coffees in the 'snug' at the bottom of her modern two-storey villa. It has a cosy, upbeat vibe – characterful and lived-in, yet tidy enough to know she really loves her space. Her dogs hang out on the terrace overlooking the infinity pool. Kristen, who is wearing skinny grey jeans, white Converse trainers, and a white T-shirt with a padlock necklace, wafts her hands towards an unemptied ashtray on the coffee table. 'This is a problem,' she says. 'As I am getting older I'm growing into my OCD. If things are a mess, I feel like I have lost everything. So I procrastinate by tidying, which is so stupid. I say to myself, "Just do what you need to do. If you want to write something, if you need to get a thought out, if you need to call someone about something creative, do it now! You don't need to organise your desk first."'

We talk more about control and she acknowledges 'once everything is taken care of I can set up a space or involve myself in a situation that I can completely and utterly lose myself in'. I suggest that this is what makes her such a captivating actress. Whether she's playing the emotionless Nia in Drake Doremus' sci-fi romance Equals or a capricious 1930s society girl in Woody Allen's brilliant new film Café Society, you believe her. In a four-star review, The Independent called Allen's latest work 'gentle, whimsical and sumptuously shot', while Kristen's performance has been widely praised, and rightly so. Though she's keen to get into directing and is this summer working on her first short – a 'very visual art film' – she still loves acting. 'I have a really strong sense of identity when I'm working,' she says. 'If I'm having a bad day, or something existential or hormonal… If anything brings me down, I'm lucky if I have to go to work that day. And that could be anything, [from a film to] a photo shoot for Chanel.' She is an ambassador for the brand and is also the face of Chanel Beauty, a role which she can throw herself into with enthusiasm because Lucia Pica, Chanel's new Global Creative Make-up and Colour Designer, is what she calls 'a friend and true visionary'. She says being around people who inspire her makes her feel 'stimulated and like I have purpose; like I'm strong, confident and feel really good. So in terms of identity, I love my job.'

Kristen Stewart Liz Collins

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What she doesn't love is everything that comes with the job: 'When I'm making a movie or developing something, I really do forget about "celebrity" and that I have some responsibility to interact with the public on what is for me a very personal level, but for them not personal at all. It's an entirely imbalanced relationship.'

She takes a drag of her cigarette and blows smoke in my face, before apologising profusely and moving out to the terrace muttering, 'I'm sorry, I'm sorry. That's awful.' I join her in the midday heat, and take in the sprawling vista of palm trees and hilltop mansions spilling into distant downtown skyscrapers.

'I very naturally do what I do,' she continues. 'The part that's not easy is addressing so many people at the same time. I know how to talk to you, but I don't know how to interact with the public because that's not one person – there's no way to personally address that entity.' What would she be like if she wasn't famous? She laughs. 'Maybe I'd be more confident. Maybe I'd have a public Instagram and be obsessed with how many followers I had, as I'd need all the attention. I'd be one of those people talking really loudly in restaurants. I'd need to perform. Actors want to be looked at. I am the antithesis of that when I'm in public. Then I'm like, "Please everyone, I don't want to exist." But there is still a strong desire in me to be seen. It's so weird.'

Kristen Stewart Liz Collins

I tell her about my interview the previous day with Amandla Stenberg. She's a young star whose fame is a result of talking directly to her fans and owning her narrative in a way that seems quite alien to actors such as Kristen who are nearly a decade older. We talk about Amandla's vlogs, in which she is open about everything, including figuring out her sexuality and sense of self. 'It's so genuine, and it's so cool,' says Kristen. 'I really admire it. Luckily, I can feel proud in a different way because I acknowledge that a whole bunch of people look at me and I live by example.'

She says she wasn't exactly hiding anything before the last few years, but feels now, more than ever, that she's 'not being taken from'. She says, 'Information is not being stolen from me anymore because I don't hide any of it. I don't care about any of the media coverage. What I care about is living in a truthful way, and I really am.' I interject to ask if 'living by example', means being open about her girlfriend. 'Yes! When I was dating a guy, I was hiding everything personal that I did because it was immediately trivialised. We [Kristen and ex-partner, Twilight co-star Robert Pattinson] were turned into these characters and placed into this ridiculous comic book, and I was like, "That's mine. You're making my relationship something that it's not." I didn't like that. But it changed when I started dating a girl. I thought, actually, to hide this provides an implication that I'm ashamed of it, so I had to alter how I approached being in public. It opened my life up and I'm so much happier.'

I'm pleased her sexuality was not the cause of any crisis of self or confusion. As a girl with a girlfriend myself, I know there's nothing more boring than getting stuck in a conversation with someone who wants to know the details of your coming out and secretly hopes there was some inner conflict along the way, or asks how 'gay' you are on the Kinsey scale, or when you first knew you were attracted to women. But Kristen and I agree that none of this matters.

Kristen Stewart Liz Collins

Not to say things have always been easy. At the height of her Twilight fame, she admits, 'I went through so much stress.' The pressure of being a young star contributed to serious physical anxiety: 'I had panic attacks. I used to puke every day and very casually too. Luckily I never suffered from an eating disorder; it wasn't to do with that. I always had a stomach ache. And I was a control freak. I couldn't anticipate what was going to happen in a given situation, so I'd be like, "Maybe I'm going to get sick." Then I'd be sick.'

So how did she get better? Did the situation change or did she change?

'I changed, that's the thing – at a certain point I realised that the fear was death, but I had gone through so much that did not kill me and… Sorry, I know that sounds dramatic. It is kind of what my short film is about – that first blow, that first awakening of realising [she shakes her head, her bleached blonde mop flopping over her eyes as she does so], "Oh, no, no, no, I'm fine." And it's only really in retrospect that I realise the anxiety just ran out. I didn't have the energy to do that any more.'

I wonder if she ever still has those anxious feelings in the pit of her stomach but she says no. 'It's kind of remarkable. I just grew out of it, but that's not to say I don't get worried.' She tells me she saw an acupuncturist recently because she can't sleep and was told her adrenal glands run at a high rate. 'I'm a highfrequency person. I wake up here [she gestures high above her head]. Then as the day progresses most people systematically produce less and less adrenalin so they are ready to sleep, but I have this fight or flight thing – I just won't come down.' She acknowledges that this is a response to anxiety, 'but it doesn't debilitate me. If I'm not sleeping, I'm fine. It doesn't worry me. I have no problem with odd hours.'

Her crew of artists and other actresses such as Dakota Fanning keep her grounded and, like all of us, she has different friends for different things. She says, 'There are people who it's so easy for me to be compassionate with. All I do when I see them is compliment them. I'm constantly like, "Dude, that looks so good on you." It works both ways and by the end of the day I'm like, "Why are we just sitting here complimenting each other. What the f*ck is wrong with us?! We obviously need this."'

Kristen Stewart Liz Collins

Most of her friends live locally, but Kristen's is the party house: 'I have one room that's soundproofed so I can play drums really loud.' She also vicariously enjoys her friends' Tinder profiles, but says, 'It doesn't happen often enough. I'm always like, "Wait, let me see!" It's so fun. I've looked over shoulders and been like, "You should say this…" and I have gone through swiping sessions, but I'll mess them up sometimes and I'll swipe the wrong direction.'

She sometimes sneaks into the back of dive bars to 'dance around with friends to stupid music', and in particular loves 'Emo night' at her local. 'It is honestly soul reviving; it is so uplifting. It happens once a month and I wish it happened more often, but it's basically a room full of 300 people all just, like, owning music that is so uncool. Nothing makes me feel better than that.' She admits to being a reluctant dancer. 'I wish I wasn't. I've had a few experiences where it's four in the morning and I'm in Paris, and I'm like, "Wait, it's Rihanna," and I'll go for it. Then I'm like, "That was so fun, why can't I harness that more often?" And it feels like something just passed me by – I had it for a second then I lost it again.'

She looks down at the 'I voted' sticker on the lapel of her black bomber jacket and now seems like the right time to ask Kristen if this marks a new politically engaged stage in her life. 'I feel a little bit more proactive. I'm not as bogged down by my work. I've been able to open my eyes and go, "Oh, wow, I live in a world that exists around me and isn't just about making movies." I was just so consumed by my work for so long. It's important to step out of that.'

So does she feel a pressure to have a 'cause' in the way Emma Watson and Angelina Jolie so passionately do? She says, 'Actually, I wish people would put more pressure on me. The more you are exposed to, the more you can funnel your power. I haven't done any of that at all yet but I understand what I could be capable of.'

In the meantime, maybe it's enough of an achievement that Kristen has survived anxiety and grown up amid a barrage of untruths, judgement and public scrutiny, emerging from it still positive, still kind, still true to herself and, most importantly, still with a sense of humour. She says, 'I have a sturdy faith in my base. I obviously hope everything going on right now will work out, but I am confident that life is good and I'll be OK whatever. In moments when that is cloudy and I feel saturated – however consuming those feelings are, they are so momentary. I'm think pretty good at being happy.' If I was her, I wouldn't whisper my name, I'd say it loud and proud. Kristen Stewart may have just voted for the first time, but in her own small way, I think she's already changing the world. ■

Interview by Lotte Jeffs (@lottejeffs)

Café Society is in cinemas 2 September

HAIR: ADIR ABERGEL AT STARWORKS ARTISTS. MAKE-UP: JILLIAN DEMPSEY AT STARWORKS ARTISTS USING CHANEL LE ROUGE COLLECTION N°1 AND LE LIFT V-FLASH. MANICURE: CHRISTINA AVILES AT OPUS BEAUTY USING CHANEL LE GEL COAT AND BODY EXCELLENCE HAND CREAM