It's perfectly normal to be worried. I remember the first time my ds stayed over night at a friend's. Only ten minutes drive away and only one night but I was phoning to make sure he was ok, then again to make sure he had eaten, then did they go to bed ok, had they slept ok... He was absolutley fine and had a great time, I was the one that was worried about nothing. the wierdest part was waking up in the morning to a quiet house and not having to get up to make breakfast etc.
If your dd is going away with school at least you know that she will be with qualified staff members, people she knows, and in a safe environment. Plus you are only 2 hours away should you be needed (you won't be). They will phone you if they need too, so don't worry about that.
And it does get easier as they do it more, but that first time is very tough.
My ds is going away in the summer for a week just him and a friend on a DoIt4Real holiday. I am still a little worried as it's the first time he'll have been away that long, and 8 hours away from home should something happen! But he is so excited and really looking forward to it. He will be fine I know that, it's me that needs reassurance! It sounds like the same with you and your dd.
She will enjoy it, you'll maybe be more upset that she doesn't miss you like mad, but she's 9 now and growing up. It's an important step for you both.
Make sure you distract yourself doing something you wouldn't usually be able to do. Go out with friends, or go to the cinema, or have a friend over for a girlie night in. You'll be looking forward to the next trip away in no time.
Try and enjoy the break. Us single parents that don't have an ex for children to visit so rarely get a break and we do need one sometimes. You'll see that once you get used to it. So make the most of the few you do get and try to relax about it! Easier said than done I know