Children being worried about entering a new school level is normal, especially if it is also in a new school building, which it sounds like this is in your daughter's case. Here are some things you can do.
1. Reassure her that all kids worry a little.
2. Encourage her to be friendly and enjoy herself in the new experience.
3. Talk to new teachers and guidance counselors to make sure they are aware of the situation.
4. Create some play dates for her to help facilitate her friendship development.
5. Stay confident yourself. She will do fine.