We took a trip last year and stayed at the Hershey HighMeadow Campground.
While they do pack the campers in tight, we found the campground to be very clean, the staff was friendly, and the befits of staying at the park were great. They have free shuttle service to and from the theme park and Hershey world. And being able to get into the park the night before for a free preview and also an hour early on the day you have your tickets is the best! We went on so many rides and saw so much before the general public was let in.... I wouldn't do it any other way!
We used the park as a home base to visit Gettysburg, and Philadelphia (that was a long day of driving) and spent one day at the park and a long morning at Hershey world before heading to Niagara falls.
If it wasn't so far for us, I'm sure we would go every year. we have been to many theme parks and I have to say Hershey was one of the very best. I hope you and your granddaughter enjoy the trip as much the DW, boys and I did!