Normally she'd offer the job to one of her brothers. But the elder one is in Glastonbury and the younger one is out somewhere.
'I'll babysit for you,' I say.
She bites her lip in an agony of indecision.
'Won't they think it's a bit odd?' she says.
I have to handle this carefully. I am absolutely knackered. Last week there were endless goodbye parties at my son's school (he's leaving in a week's time), and I can think of nothing better than spending the evening sitting in someone else's clean and tidy sitting-room watching my choice of TV (i.e. no Top Gear or violent films about serial killers).
But I can't sound too desperate. Otherwise the whole thing might backfire and she might insist on going herself.
'It's my end-of-exams present,' I say. 'I'll do the job and you'll get the money.'
Eventually, with great courage, she makes the phone call. The family is fine about the last-minute change of personnel. Off she goes to her friend's house, smiling from ear to ear.
Later, equally smiley, I set off to babysit.
What I had forgotten, of course, is that I'm no good at remotes. There are three of them, all black and shiny. The lovely 11-year-old goes through it all and says goodnight. Twenty desperate minutes later, I call him down again.
Patiently, he runs through the whole thing a second time, and disappears back upstairs. It's late. I sit there miserably watching the only thing I can call up – a repeat of Nigella cooking peaches.
I text my 18-year-old. 'R u back?'
My 18-year-old comes over. Within seconds he's mastered all the remotes and has a choice of a million channels on the screen.
'You go home, Mum,' he says. 'I'll stay here till they get back.'
As I trudge back home, I think, teenagers rule the world.
These days, I can't even babysit.
Does this sound horribly familiar?
Do you struggle with other people's remotes when babysitting?