The Blue Cheese Incident should have tipped me off about my middle child, but it didn’t.

Possibly because Baby Deux had been rebellious from the start. My swag at having raised one gender-neutral, early-reading, easy-to-negotiate-with, sure-we-can-still-make-spontaneous-plans! child vanished overnight. Instantly different from her older sister, she challenged some of my basic beliefs about how to raise daughters from the start. Within a few years, our house was infested with Barbies, fairy wings, a pink wardrobe and a large percentage of China’s GDP in rainbow-hued plastic jewelry and ‘high heels.’

Her asthma meant she was often out of school, at home, trying to wheedle me into buying her more pink things as I struggled to maintain a career. She developed a melodramatic personality that amused and entertained our friends, who indulged her, but, by age 9, had me furiously Googling ‘hormonal shifts in pre-puberty.’ I got sassed and challenged on a regular basis.

“It’s a phase,” I reassured myself, “I must have forgotten that I went through this with the elder one.”

But I hadn’t. And I had no idea where it was coming from now. There were no physical signs of adolescence, but Baby Deux, now an 11-year-old middle child, was precocious in every other way. So, given that nature wasn’t the obvious cause of her tendency to talk back in ways that even made her older sister gasp, I decided not to take any chances with nurture: I parceled out alone-time with each child, praised each as individuals, never compared and constantly reminded my second child that there were theories that suggest an age gap of more than four years (like the one between her sister and her) actually nullifies middle child syndrome.

It got better.

She started playing sport and grew healthier, more confident. She befriended the younger sisters of 15’s besties giving her a posse and ‘status’ with her tween peers. She dropped the tutus and Barbies and started dressing more like a person and less like a gregarious unicorn.

It got worse.

She threw massive sulks at imagined slights, acquired terrible social FOMO and then did an unprecedentedly rebellious thing: She made me the straight guy when telling funny stories. “And mama, she’s sooo uncool, she was like….”

Was my personality changing? Had I only imagined parenting a tween was easier with the eldest? Should I have relied on the sibling birth order theory (even though it’s increasingly viewed as inconclusive) and settled back into the rough assumption that the eldest will conform, the second will rebel (and the third will be a slacker)? How do you explain why two (or more) children with the same biological parents differ so much from each other?

Then the Blue Cheese Incident happened. No one eats blue cheese in our house except me. There have been offhand comments about how my occasional (okay, habitual) tendency to lapse into foul exclamations has turned my taste buds impervious to other sharp tastes. But on our first lunch on holiday this summer, I looked up in alarm as my 11-year-old reached over and cut herself a big hunk of my Gorgonzola.

“Err… that’s mine,” I said.

“But I love it,” she said — and went in for some more.

Since when?

People play that nature/nurture lottery game with the kids, usually to compliment themselves – “She gets her Maths skills from me,” “Oh, he’s sporty like his dad” – or diss the in-laws. (“You are whining exactly like your dad’s great-grandmother!”) After the Blue Cheese Incident, I admit I beadily eyed the extended branches of my husband’s family tree trying to find one craggy enough to hang my second daughter’s tendency to one-upmanship, a sharp tongue and strong opinions on.

I couldn’t get a handle on my middle child. On holiday, she was the one to initiate more adventurous excursions with her 15-year-old sister – going to buy a granita or some tourist tat, or smiling back at a couple of handsome 12-year-old boys on the beach – and she brought this desire for independence and autonomy back home. It works well in some cases. She walks home from the school bus stop alone and unperturbed on days our schedules are out of sync. She meets new kids and challenges with optimism and enthusiasm.

In other cases, though, she harangues me into letting her have an Instagram account and stands up to a someone “bullying” her older sister online, causing absolute mayhem in their social circles.

I was floundering even when an old friend, having spent an hour bemusedly watching her antics, drawled at her, “Ah, you’re just like your mother. Even she thought she was a boy.”

No, the puzzle only fell into place recently. Exasperated by her usual ranting about something, I asked her to stop using the word “annoyiiinnng.”

“You’ve said it about 30 times, already,” I snapped.

“What’s it to you? Why can’t I say it?” she shot back.

“Because it’s annoyiiinnng!” I said without thinking. Then I bit my tongue.

She’d perhaps been conforming more than I thought.