Oh dear, what can the matter be?
From which she would emerge, much relieved, to say the school loos were - pee-uuw! (Theatrical pinch of nose and much gagging.) There was wet in the floor, she said, and they smelled, and none of the girls ever went in there unless they had to.
In fact Hannah Jarvis hadn't been in there once, not ever, and she was nearly eleven and had been at the school since Year Three!
Apart from the medical consequences of such daily continence - we once had a family doctor who lectured us sternly on the dangers of travelling in a car with a full bladder (crashes, ruptures) - I was sorry he felt so troubled by her daily environment.
Yet the mild whiff of a junior school toilet is as nothing to some of the hell-holes that pass for lavatories in secondary schools.
I know because I've seen plenty - quite enough to know that graffiti and cigarette burns, scratched walls and broken locks and littered floors, are all par for the course, and that the squeamish should never think of crossing a cubicle threshold without a precautionary poke-and-peer.
One outer-London teacher remembers a boy who, when nature called, was so unable to bring himself to make contact with the seats provided, he felt quite justified in quitting school and heading for home.
Yet although school lavatories don't seem to figure in the consciousness of the educational great and good, and probably only register in most teachers' minds as places to avoid, to pupils they are more central to their day than any hi-tech science block of state-of-the-art computer link.
They are - in a way that nothing else is in school - their own private space; their kingdom; the one place where they can rule supreme.
It follows, therefore, the state in which they are kept tells students everything they need to know about how their school values them.
In fact, in this season of open days, parents anxious to find out the raw truth about any school would do well to bypass the fancy design and technology displays and check out the lavatories.
This happened, inadvertently, to a friend who took her son to look round one of her local comprehensives. While she listened to a presentation of the school's curriculum, he went off to use the loo, where he found stalls with no loo paper and sh-you-know-what smeared on the walls and floor.
Not surprisingly, he wanted nothing more to do with the school. What he had picked up, said his mother (in an unfortunate turn of phrase) was not merely that the lavatories were revolting, but that this was a threatening environment which would not care for him, or keep him safe.
Although, I've never fully understood why school lavatories get as grotty as they do. I'm sure most children - give or take the seriously disturbed few - don't go home and chuck unmentionable things onto the floor behind their own loos, or gouge holes in their bathroom walls, so why do they do it in school?
Probably because, as one teacher suggested, it's the obvious place to let out aggression and resentment, to lift two fingers to school rules, and indulge in off-limits behaviour. A metaphorical sewer as well as an actual one.
If that's true, then any graffiti are, quite literally, telling - wall newspapers reporting on the state of esteem between schools and their clients.
But maybe it's something far more prosaic. As keeper of our own domestic offices, I know what hard, repetitive and thankless work it takes to keep sinks and loos clean, how much nagging is needed to make all users adhere to a common code - and just how quickly the untended slides into the squalid. And who, in school has either the time or motivation for all that?
Yet schools try. At my daughter's pee-uuw primary school, student governors drew up schemes to encourage their peers in the sociable arts of flushing and hand-washing.
The question is, is it hard enough? I once visited a failing school in Hertfordshire, short of every conceivable educational resource, where the first investment by the energetic new head brought in to turn it round had been the refurbishment of the girls' loos, complete with sumptuous decor and well-lit mirrors.
It was a controversial move, not least among the staff queuing outside his door to beg for essential supplies. But who, he asked, was the school for? The students. And where did they - particularly the girls - choose to spend their free time? In the cloakrooms, that's where. In front of the mirror.
By acknowledging the realities of their world, and honouring them, he felt he was sending out a powerful message about how this new school would treat its students, and what, in turn, it would expect of them.
Sometimes simple familiarity can breed complacency.
Some Swedish friends of ours recently visited Britain and, staying near where we used to live, were delighted to accompany their hosts' children to the same school where my own children once went.
What did you think? I asked Eva, enthusiastically. Did you go in? Did you see the artwork? Did you see the nursery? Did you see the children's garden?
Oh, she said. It stank. How can anyone send their children there.
I was speechless. This was one of the most sought-after schools in the area. Parents queued round the block to get their children in. Then I thought back. The Victorian building had always had a problem with its boys' loo, and no amount of disinfectant had ever been able to mask the aroma of centuries-old pee.
But if you went there every day you got used to it. After a time you even grew fond of it. It seemed the very essence of school life, along with the smell of polish in the hall and steaming gym shoes in the cloakrooms.
Not to Eva, though, coming from bright, clear Sweden. To her it simply stank. It was a disgrace. An insult to our children.
And maybe she's right. Maybe our standards are far lower than they ought to be.
So I offer school heads the Eva challenge. Tour your facilities with her eyes. How do they measure up? Look at them through your own. Would they do for you? And, if not, why are they good enough for pupils? And if the answer is, they aren't, then surely the next questions have to be: why not? And what, if anything, can be done?