If you are making the change next september...You could try to going to some of the schools events during the rest of the school year. That would help her feel more familiar before school starts. If there are any camps this summer that would also help her get to know some kids before school starts. Do you know any other families at the school? Would she be open to some playdates?
Academically...I would talk to her about what to expect so it's not a surprize. Let her know it's ok to make mistakes, that is apart of good learning.
