At a PEN lecture in Manhattan last weekend, the novelist Chimamanda Ngozi Adichie took Hillary Clinton to task for beginning her Twitter bio with “Wife, mom, grandma”. Her husband’s account, it will surprise no one to know, does not begin with the word “husband”. “When you put it like that, I’m going to change it,” promised the 2016 presidential candidate.

Adichie is an international bestseller and about as starry as a writer can be (when we meet she chats casually about recently meeting Oprah Winfrey, who made a little bow to her). Her first novel, Purple Hibiscus, published when she was only 26, was longlisted for the 2004 Man Booker; she won the 2006 Orange prize for Half of a Yellow Sun; was awarded a MacArthur fellowship – the so-called genius grant – and her work is now a fixture on American school reading lists. Following her sensational 2013 TED talk, We Should All Be Feminists, (sampled by Beyoncé, used by Dior for a series of slogan T-shirts and distributed in book format to every 16-year-old in Sweden) the 40-year-old has become something of a public feminist: hence scolding the former US secretary of state.

The atmosphere at a recent event with Reni Eddo-Lodge (author of Why I Am No Longer Talking to White People About Race), part of the Southbank’s WOW: Women of the World festival in London, was more like a party than a books evening. The excitement among the audience of largely young women was as striking as the amazing hair and outfits (“That will be the Nigerians,” Adichie says proudly). The two writers received a riotous standing ovation before they had even sat down. As festival founder Jude Kelly said in her whoop-inducing introduction, “The world is changing very fast, and we intend to accelerate it.”

“I feel optimistic. But cautiously optimistic,” Adichie says of the #MeToo movement when we meet a couple of days later. “It’s either the beginning of a revolution, or it is going to be a fad. We just don’t know … I do see in women a sense that ‘We’re done, this is it ... No.’ and it gives me hope.”

I feel lonely in my fight against sexism, in a way that I don’t feel in my fight against racism

Adichie lives in both Maryland and Lagos: “I couldn’t be happy living entirely in Nigeria or living entirely in America.” She “became black” she says, when she moved to the US as a student, and the experience of being black but not American is bitingly captured in her much loved last novel Americanah.

But now in Dear Ijeawele: A Feminist Manifesto in Fifteen Suggestions (just published in paperback), she writes that she is angrier about sexism than she is about racism. “I don’t think sexism is worse than racism, it’s impossible even to compare,” she clarifies. “It’s that I feel lonely in my fight against sexism, in a way that I don’t feel in my fight against racism. My friends, my family, they get racism, they get it. The people I’m close to who are not black get it. But I find that with sexism you are constantly having to explain, justify, convince, make a case for.”

Written just before the birth of her own daughter, the manifesto began as a letter to her friend, who had asked for advice about how she might raise her baby girl as a feminist. “Teach her to love books”; “it is important to be able to fend for herself”; make sure dad does his share of the nappy changes – some of the suggestions may seem obvious, and the author’s dismay on discovering that baby clothes come in, yup, blue and pink, and that the toy aisles are divided into trucks or dolls, feels a little disingenuous. But it’s hard not to be won over by the big hearted ambitions of this tiny pamphlet. Simplicity and accessibility are the point: Adichie is not preaching to the converted; she doesn’t do “jargon” and finds the classic feminist texts “boring” (“Do you think The Second Sex is interesting?” she shoots back, when I press her). Although the “you” in the letter is “Ijeawele”, a Nigerian mother living in a traditional Igbo culture, Adichie is talking to young women the world over: “To get letters from women, saying ‘you make me feel stronger’ that means a lot to me,” she says. “It’s a woman in Denmark, it’s an email from a woman in Korea, it’s the woman in Ghana. I can’t tell you how happy that makes me.”

Facebook Twitter Pinterest ‘Blackness and whitenes are different’ ... speaking at London’s Women of the World festival in April. Photograph: Jack Taylor/Getty Images

One of the most compelling injunctions in Adichie’s manifestos is to encourage girls to “reject likability”. “Oh my God, all that time wasted,” she says with feeling, that boys and men do not waste. Clinton and “all the harping on about whether or not she is ‘likable’,” is the perfect example of how she had to persuade friends that sexism was at work. “It is still very upsetting to me. I don’t care how much societies tell themselves that they are progressive, the kind of criticism that Clinton gets from the very progressive left, I think is terrible. People now say to her ‘shut up and go away’ – that whole idea of silencing women. I kind of like what’s happening to her now, it feels as though that ‘fuck it’ I wish she had said before, she seems to be saying now.”

One group who didn’t seem swayed by how much they found Clinton likable was black American women, 90% of whom voted for her in the election. “Trump’s campaign was coded, but it was the language of racism, the language of taking the country back, being anti-immigrant in a way that was being opposed to immigrants of colour,” she says. “There were white women who were therefore able to overlook his very blatant misogyny because he appealed to their whiteness.”

Unsurprisingly, language, for Adichie, is a feminist issue, at its most insidious when it comes to pregnancy and parenting, a verb she dislikes. She rages against terms such as “baby bump” as “diminishing”, preventing proper discussion of serious issues such as the gender pay gap and maternity leave. “There are so many women for whom pregnancy is the thing that pushed them down, and we need to account for that. We need to have a clause in every job that a woman who gets pregnant gets her job back in exactly the same way. It’s wrong!” For her, gender is a social construction: “I don’t think I’m more inherently likely to do domestic work, or childcare ... It doesn’t come pre-programmed in your vagina, right?”

Feminist is a bad word, everywhere in the world, let’s not kid ourselves, but particularly where I come from

Although she put on “the feminist hat” quite happily, she never intended to become a voice for feminism, “then it happened”. She expected a degree of hostility – “Feminist is a bad word, everywhere in the world, let’s not kid ourselves, but particularly where I come from.” But she was not prepared for the furore that followed an interview on Channel 4 last year when she sparked controversy by arguing that the experiences of trans women are distinct from those of women born female, which was interpreted by some as “creating a hierarchy” and implying that “trans women were ‘less than’, which I was not ... I don’t think that way.”

She was “genuinely surprised” by the outcry, “because I thought I was saying something that was obvious”, she says and remains defiant on the importance of acknowledging difference (the final, heartfelt message of Dear Ijeawele): “The vileness that trans women face is because they are trans women – there are things trans women go through that women who are born female will never have to go through … If we are going pretend that everything is the same, how do we address that?” She compares this well meaning wish to be inclusive with claims of colour blindness: blackness and whiteness are different, she told the audience to huge cheers at the event with Eddo-Lodge. “Yes, we are all of the human race but there are differences and those differences affect our experiences, our opportunities,” she says now. “There’s something about it that I find inherently dishonest.”

Facebook Twitter Pinterest Adichie grilling Hillary Clinton at PEN America’s World Voices Festival in New York in April, 2018. Photograph: Karsten Moran/New York Times / Redux / eyevine

She was accused of “killing trans women with her words” and, she says, there were calls to burn her books; she was particularly hurt by the online response from some of her former students on her creative writing workshop in Lagos, where trying to break down taboos about gay rights and women is as important to her as the teaching. “I was told, ‘you’re being shamed’,” she gestures the inverted commas of internet shaming. “When somebody is shaming you, you also have to feel ashamed. I just didn’t. I was upset. I was disappointed.” She feels her “tribe”, those “generally of the left, who believe in equal rights for everyone”, let her down: “I thought surely they know me and what I stand for.”

Looking back, she thinks her “major sin” was that she “didn’t abide by the language orthodoxy”. At the Southbank event the author, who is not on Twitter (“there’s an ugliness about it”), expressed her reservations about “a certain kind of youthful, social-media savvy feminism that is not my home”. She is wary of the term “intersectionality”, but is clear as to what it does not mean, recalling an interview with a white actor who, in her anxiety to acknowledge the sometimes racist history of western feminism, claimed it was not about her, but about black women who had been oppressed. “Of course feminism is about her,” Adichie says with exasperation. “I wish she’d said: ‘Here is all the shit I get because I’m a woman, but I think about all those other women who don’t have the white privilege I have, I can’t imagine what that must be like.’ That for me would be perfect.”

While she is frustrated with what she identifies as a “quickness to outrage” among young people – “it’s boring” – her real anger is reserved for the progressive left, especially in America, which she believes is fostering this unforgiving atmosphere, closing in on itself and closing down essential conversations (“Shut up, you are wrong” ) in its haste to assume ill will. Displaying a “fundamental lack of compassion”, it goes against her credo as a storyteller, in which all human beings are flawed: “There’s no room to be righteous.”

Despite all “the noise” of the last few years, fiction remains her “religion”: “I really do believe I was born to do this.” In an interview with her friend the novelist Dave Eggers last year, she said she was “no longer the dutiful daughter of literature”. She’s having fun, discarding the rules and increasingly blurring the boundaries between fiction and memoir.

“Because we write fiction we mine our souls. Of course you put yourself into your fiction, your fiction is you.” All she needs is solitude, silence and space in which to write. “It’s exquisite, the joy. Even just talking about it I almost want to cry,” she says, blinking. But when the writing is not going well, “I go into this terror of thinking that I might never write again. That’s the one thing that terrifies me”