OP, I completely sympathise. I spent many years battling with anxiety about something happening to my DC. I had counselling for emetophobia and while it didn't help much with the emetophobia, it did enable me to see more clearly that the thing I was really, really terrified of was the DC coming to some kind of harm. The first time DC1 went on the school minibus, for a journey of about two miles, I spent the entire time listening to the local news, expecting to hear that there had been a minibus crash.
In my particular case, I was sort of forced out of it by a hideous separation and divorce, court case etc. I had to focus on that so much that I just found myself focussing less on the rising panic that used to grip me even just walking down the pavement (what if a car mounts the pavement and hits one of the DC? And so on...)
I think that now they are older (university, boarding school, independent teenagers at home), I have just had to trust that the vast majority of people reach adulthood. It feels a bit like jumping out of an aeroplane without a parachute, but I couldn't bear my DC to feel anxious in the way that I have done, so I have just had to let them get on with it. They travel around and even the youngest has flown alone (if anyone had told me I would permit this when DC1 was small, I'd have bet them a gazillion pounds that I wouldn't. How things change...). Some of the things the older ones have told me after the event would have floored me at the time, so there's also something to be said for them getting older and somehow thriving. I also found it all slightly easier with DC2 onwards. Though if I started to think about it now, I'd get that awful cold, sick feeling - so I won't.
If you can afford this trip (and affording them is a whole other kettle of fish: I've said no to several that "everyone else" is going on as I can't afford them), I think you should overcome your fears and let your DD go. Wave her off happily, then weep on a friend/family/your OH, if you have one.