I have no doubt that I would have had the same reaction as your DD...excited when I got there, but in tears by the first night. It's got to be completely overwhelming.
(I actually cried on my first VACATION to WDW just because I was overwhelmed by traveling all day, not eating regular meals, and being all the way across the country for the first time. By the second day, I was ecstatic to be there of course!
)
It is only natural for you guys to worry...no parent wants to hear their kid in tears and know that they are far away on their own!
She will be great, just give her some time...maybe send her a care package with some of her favorite things, whether it be some sentimental items from home, or just a few of her favorite snacks. The littlest things will make a big difference while she's settling in!