Forty years ago this month, Germaine Greer's The Female Eunuch was published – and women's liberation would never be quite the same again. Generations of feminists have been inspired by Greer's belligerent, bile-spattered dialectic of rebellion, a 400-page brick slammed through the screen of male entitlement and female submission. At the age of 12, I was one of her youngest devotees, and although today I take issue with many of her conclusions, the book still thrills me to the core on each rereading.

I spotted a worn copy of The Female Eunuch on my mother's shelf in 1999, and something about the savage cover, showing a hollow female torso with handles hanging from a clothes-rail, seemed to whisper a wealth of dangerous secrets. Like a grimoire in a fairytale, I felt drawn to the book, somehow compelled by it. Leafing through the yellowing pages I realised, with the righteous rage that only a preteen can summon, that I had been lied to. There were other ways of looking at the world. There was more to sex than the sterile, ritualised commercial play my classmates were already rehearsing, more to femininity than the smiling servitude that made my mother and grandmother so unhappy. In later life, I would come to understand this process as consciousness-raising; at the time, it felt like a striplight had been switched on in my mind.

Being a conscientious kid, I immediately got out my best pens to write a letter to Germaine Greer telling her so. Two months later, a package came through the door, containing a postcard with a pair of friendly-looking koalas on it. She had replied! I was in raptures, and vowed to devote my life to feminism. Like any earnest prepubescent convert, I took my devotional text extremely literally. Greer advised all women to taste their menstrual blood in order to combat genital horror – so when my first period arrived, I dutifully did so. It was salty and sour, but not shameful.

Reading The Female Eunuch as a child in the perky "post-feminist" years of Blair's Babes and Girl Power, I thought I was the only girl alive who still believed there could be more to womanhood than wearing a great dress and smiling for the camera. Well – almost the only one.

In 2001, on a sweltering, sticky coach trip with the local youth orchestra, I was fumbling in my rucksack for a packet of Wotsits when my copy of Greer's book fell out and skidded under the seats. As I scrambled nauseously on the shaky coach floor, I felt a hand on my shoulder.

"Here's your book," said a girl behind me. "Um, are you a feminist?" she said. "I am too. I thought there weren't any others our age." From that moment on, she and I were inseparable. We spent two heady summers sharing secrets, plotting to overthrow patriarchy and holding hands shyly whilst listening to riot grrrl punk on a shared Walkman.

By Greer's standards, we were hardly daring, man-eating sexual revolutionaries, but we wanted to change the world as only teenagers can. Now that I'm grown up, with my own book coming out next year, I know that to create an honest, adult politics of change, one must first interrogate one's idols.

Of course, there are problems. As a child, I thought The Female Eunuch had been written just for me – and as it was targeted at bourgeois, well-educated white women living in rich western countries, it practically had. Unlike many middle-class feminists, Greer never claimed to speak for anyone who did not share her background. Unfortunately, the more time I spend with feminist activists, the more I wish she had at least tried. Had strident, second-wave, sex-positive feminism like that espoused in The Female Eunuch been more inclusively phrased, the ghettoisation that still dogs contemporary women's activism might have been avoided.

Another uncomfortable failing of the text is Greer's savage attack on transsexual women. Greer has long led the radical feminist charge against trans women, whom she labels "castrates", fifth columnists mocking real women and invading female space. This is an ugly untruth, and has directly influenced the bitter, childish rows over the status of trans women that still scar the modern feminist movement. Just recently, an angry debate has erupted yet again over whether or not trans women will be welcome at the annual Reclaim the Night march against sexual violence, threatening solidarity among the new generation of activists.

As a child, The Female Eunuch was my bible, but if feminism is to remain a living, breathing, vital movement, we cannot afford to have sacred texts. It is vital that every cohort of feminists remains in a dialogue with its antecedents. Germaine Greer's rage and revolutionary energy resonate across four decades of feminist activism – but we can still question our foremothers, and we should.