About five years ago a friend at my son’s school, a girl of 14 I’d only met once before (and liked very much, with her big eyes and cheeky smile) got herself into something of a crisis, and as a result of a breakdown in her home life, came to live with us. I hadn’t been looking to add another child to the family. We had our son at home, also 14, and my older son, aged 25, from a previous relationship was finally moving out. Suddenly, at 52, right when I thought I was done with mothering, I had a brand new teenage daughter.

The social workers asked me the most prying questions

I was plunged into a world that had previously been unknown to me: social workers, foster training, adoption panels, mental health professionals, monthly supervision… and that’s not to mention the pets that our foster daughter brought to the household: three rats, Becky the gecko, Eliza the lizard, two guinea pigs and latterly a corn snake (this one is a very beautiful iridescent lemon colour, of fascinating muscularity. Like so many things about this experience: not at all what I expected).

I had an exhausting number of interviews after I made the decision to apply for a long-term foster placement for our daughter. Actually, it was jointly agreed, my husband is very involved, and our other son, too, but in the early formal dealings it felt to me to be much more about me, and my fitness or lack of it for the task.

It is bizarre to recount your life from birth to the present to a stranger who is taking notes and trying to decide if he can recommend you to be a foster parent to a panel of experts. I found myself saying, more than once, “I did want kids yes, but um actually, what I really wanted was to be a writer…”

Although the social workers asked me the most prying and startling questions (“Are there any sex toys in the house?” “Can you guarantee that there is no porn on any of the devices that anyone in the household owns?” “Have you ever terminated a pregnancy?”), they were singularly uninterested in any discussion of my life outside the home: the things that matter immensely to me and are probably the greatest indicator of who I am.

Given that my foster daughter is conscientious and clever and had from the first time we met said that she hoped to work in politics, I assumed it relevant to mention my professional life, because it might offer her some kind of role model. But no. We might have been in the 1950s: their entire definition of me was as a mother. It was a sensation I hadn’t felt in a while. For 25 years, to be exact, since my first son was born.

I remember his tiny little form, squirming and yelling, placed in my arms at Homerton hospital in Hackney, and me thinking, “I guess I’m not the maternal type – blimey! Can I do this?”

Where do we get the idea from that there’s a type? Back then, I consoled myself by reading Adrienne Rich’s fabulous Of Woman Born and decided that this was the only guide to motherhood I needed. Rather than being defined as mothers, or by their status as childless, women should be defined in terms of themselves, as all humans should be, claimed Rich. Nor should becoming a mother mean women are isolated and not allowed to participate in the social and professional world. Instead, Rich called for “a world in which every woman is the presiding genius of her own body”.

The qualities needed as a foster parent (commitment, a sense of humour, empathy, kindness, imagination, resilience, advocacy skills, flexibility) are just as likely to be intrinsic personality traits or skills gained in working life than acquired by the mysterious route of becoming a mother. I was asked, during one of the most searching and tiring of my social worker interviews, had I ever cared for a child who wasn’t my own? A stepchild for instance, which is, after all, a very common experience. I shook my head.

I learned that I could indeed feel love for a child that wasn’t mine

And then suddenly I remembered Connor – a child I looked after on graduating from university, years before my own son was born. I worked as an au pair in the early 1980s for two different families in London and in one of them, I found myself taking care of a five-year-old boy whose mother had recently died. He was very lovable, blond and cuddly, but he would sometimes stop mid-sentence to ask, heart-breakingly: “Where is Mummy?” Once, he told me: “I have a film running in my head and Mummy is in it.” He would rock himself to sleep, bashing his head from side to side in his bed, and then abruptly sit up and stare and scream that Mummy was in the room with us. Although I hadn’t thought about Connor in a long time, that experience, of being invited into the imaginative world of a grief-stricken five-year-old, had been sad and indelible.

My latest novel, set 10 years earlier in the 1970s, inspired by the murder of Sandra Rivett, nanny to Lord and Lady Lucan, tells the story of two young women coming to London to work as nannies. Like me, their main motivation was to escape their boring lives in a small village, ironically to escape, too, the prescribed route of wife and mother, and have independence, adventures and romance in the big city. One of the girls is a Norland nanny, but the other, Mandy, probably hadn’t thought that hard about the huge responsibility for the emotional wellbeing of the children in her care that foster parents are quite rightly grilled about.

For young women, being a nanny has the added appeal of being provided with a room in a home, perhaps a car, too, as well as an income. What many don’t anticipate is how intimate the experience will be; how you will be dunked at once into the emotional soup of the family you work for. A foster parent, meanwhile, is offered ongoing supervision by a social worker and some training, but I think real support comes from the networks you have already set up by the time you reach my age. How glad I was to be older, with all that genuine experience under my belt. Energy, a partner I can talk things over with, sharing the emotional ups and downs, good health and good friends have proved more useful than any “training” or preparation for the role.

These days I also know how to ask for help where needed from others – mental health professionals or friends – something I was reluctant to do when younger.

Five years along, the emphasis in supervision on “independence” and preparing my foster daughter for adulthood has made me more conscious of doing the same for my teenage son, too. This means they both do their own washing, can cook a decent meal, budget for a weekly shop and get themselves to places by bike (him) or car (her) without asking us for lifts or money. We are no longer deemed foster carers but “supported lodgings providers” under an excellent local authority scheme which provides young people aged between 16 and 21 with a room in a friendly home and the support and guidance of an adult living there.

Anyone who has reached adulthood knows the veering between adult and child that happens during adolescence and how many things can go wrong. Those in the care system are hugely disadvantaged by this lack of a home, support or safety and the outcomes for such young people reflect that vulnerability, with a shocking 25% of the homeless population having been in care as children. My daughter, now 19, is among only 6% of care leavers who will go to university. Getting a place at university is all her own doing – she’s determined, clever and hard working – and our pride in her is intense.

Still, looking after a child who is asking questions you don’t have answers for, or has experienced loss or trauma, will always be a testing experience. A child’s nightmares sometimes seep into yours, too. That first little charge of mine, Connor, did teach me that I had some mettle I could draw on in emergencies. He taught me – as I discovered with my daughter, too – that I could indeed feel love for a child who wasn’t mine.

But of all the probing questions the interviewer asked me to determine my suitability as a foster parent, love, the most important word, was not mentioned at all.

Jill Dawson’s novel, The Language of Birds, inspired by the sensational Lord Lucan case, is published by Sceptre at £18.99. Buy a copy for £16.71 at theguardianbookshop.com