A journey into the unknown as my daughter turns 13

This weekend my firstborn turns 13, and I will round a symbolic corner, bracing myself. How did this happen? Years leapfrogging over each other in a whirr of dinnertime, deadline, supermarket shopping, pick-up and drop-off, until here I am, the mother of a teenage daughter. Here I am even as my own adolescent self continues to shadow me – ribbing, goading, demanding – openly contemptuous of what my reflection in the mirror insists is true.

And as if on cue my daughter has in recent weeks exhibited an unambiguous sign that she's passing from the cheerful restlessness of little girlhood to the next stage. It is not the plastering of Selena Gomez and Ariana Grande over her bedroom walls, or that she's sleeping in for longer on the weekends or that she's peppering her speech with phrases such as "she was really pissed about that".

No, it is the sudden flowering of friendship; close, all-encompassing friendship. This relationship is qualitatively different to the feverish-but-fickle attachments during the primary school years when one week girls declare themselves "BFFs" only to kick and break up over something trivial the next.

Teenage friendship between girls resembles a new romance. The need to see and talk to the other is urgent and near-constant; the fidelity remarkable. "Can we go to the new Chadstone, mum? And tomorrow can we go to the beach?" Sleepovers stretch to the following evening.

Thumbed text messages all the way to bedtime. Nicknames. Giggling. The unconscious mimicking of the other's gestures and cadence. I'm reminded of the Anne of Green Gables series, which I devoured as an adolescent, in which the red-haired Anne falls almost instantly in love with the raven-haired Diana, her "bosom friend".

It comes as a relief that I've been usurped as the central character in my daughter's life. (Maybe this is the last time I can marshall her in the service of a column: "until adolescence," writes British-based novelist Rachel Cusk, "parents by and large control the family story".)

Among the many fears I've been nursing about her impending teenagedom – the roll call of dangers from risk taking to taking no risks at all – was the fear the digital age might stunt her relationships, never mind the even greater fear of cyber bullying and the toxicity of which teenage girls are uniquely capable.

Everything I read seemed to heighten this fear about emotionally superficial teens. In 2009 the Archbishop of Westminster, Vincent Nichols, warned the collapse of friendships – due to "transient" internet relationships – could leave young people feeling suicidal, and even though I'm an atheist the idea embedded itself in my consciousness.

And I can see what's happening to me. As much as texting, social media and email let me build elaborate networks they also help me hide; efficient communication has replaced rambling conversation that was occasionally inconvenient and frustrating but also fostered patience, empathy, give-and-take.

As a teenager the hours I spent with girlfriends, giggling and whispering confessions on the phone, hanging idly in the park, helped me figure out the world and my place in it. "This conversation is so deep I'm sweating," I remember a friend breathing down the phone when we were 14 or so.

That particular friendship did not endure into adulthood. And even with the friendships that have lasted the distance the intensity has faded. Sometimes I think the untold grief of adulthood springs from a longing to recreate this faded intensity; I'd wager that for most women their later relationships with adult partners cannot replicate the emotional intimacy of these girlhood friendships.

It is no surprise the Neapolitan Quartet, the four novels written under the pseudonym Elena Ferrante – whose identity was recently and rudely outed by an investigative journalist – became an international bestseller largely through word-of-mouth from women.

The novels, which track two childhood girlfriends across a 60-year period of postwar Italy, capture so vividly the closeness and complexity of female friendships, the love, rivalry and centrality of the relationship amid changing fortunes, political instability, children, marriage and divorce. I reckon it's Anne of Green Gables for grown-ups. Anti Safe Schools campaigners avert your eyes now: when it comes to matters of the heart, a great many women are basically lesbian.

I cannot measure the intensity of my daughter's friendships against those of my own teens when social life was less expansive, and who says depth equates with happiness anyway? The flip side of closeness is vulnerability. I can still feel the indignation and panic I experienced as a teen when I sensed another girl muscling in on my special friendship.

I still wince at the cruelty I was also capable of – pitting friends against each other, betraying confidences, secretly wishing for another's humiliation. Despite my children growing up in prosperity and relative peace, at a time when we've never been healthier or lived longer, fear, about everything and nothing, still gnaws at me. But I let go, gently.

The other day a friend – a dear, childhood friend – told me she had spotted my daughter in the neighbourhood. "She was sitting on a bench outside a chemist with another girl," she reported, "her friend, I assume?"

"Yes," I said.

Julie Szego is a Fairfax Media columnist.