Does make me feel sad that she doesn't want to be with us anymore.
It's part of the letting-go. Yeah, it's dismaying.
We solved it by making ourselves the Sleepover House. (This is not, incidentally, because we're nice people. It's at least in part because one of our daughters has a chronic illness that makes it difficult for her to stay over at other houses. So we either have sleepovers here, or she doesn't get to do it at all.)
It costs us a few bob in chicken nuggets and crinkle-cut chips, but we like to know where our daughters are, and (fortunately) all their mates are polite, considerate and grateful.
I mean, I don't think this is necessarily a solution for everyone. Not all parents want a gaggle of teenagers in the place, even if they're all up in the attic bedroom out of the way. And you do have to listen to the thumping basslines of a lot of dubstep.
But, for me, this strategy was justified last month, when there was a knock on the door at lunchtime. It was a kid who'd had an accident at school - he'd cut his hand really badly. The school got him to A&E, where he'd been stitched up and given strong painkillers, and then he was taken back to school. But the painkillers meant he was pretty much out of it, and he was told to go home.
He realised, having left school, that he really needed the loo, and he felt faint. So, as he was close to us, he knocked on our door.
"I'm really, really sorry - but could I use your toilet?"
And I thought, "This is good. We're regarded as the safe place that people can go. And all it has cost us is Iceland goujons and an inexhaustible supply of Pepsi Max."
This looks like a stealth boast, doesn't it? It's not intended to be. It's more that teenagers need to socialise, need to feel connected to a group, need to learn to be grown-ups in a place that allows them to be kids. So parents have to provide them with circumstances that allow them to do that - to the extent that it's practical.
We're lucky, because we can. Some parents can't. If you can, OP, then get yourself on the sleepover circuit. And if you can't, I think it's worth checking out who they're staying with and whether you think it's okay.
Which, I know, is easier said than done.