The school which my 2nd grade daughter attends has the students meet the next years teacher and students a couple of weeks before the end of the school year. They've decided on the class roster before the end of the year. It might help if you asked the school to allow your daughter to attend that get together. If that's not possible the school's office should be able to put you in touch with her new teacher and some of her classmates if you contact them before the teacher's last day and the office closes for the summer.
I think it's an excellent idea to put your daughter together with students in her grade at her new school. You should be able to get a copy of her new classroom's class roster.
I'm assuming you know which school she will attend. If you live in the same neighborhood as the school (assuming the change is not the result of you also moving into a different home)you could talk with your neighbors who have children and get your daughter involved with their kids. Also go to the playground in the summer. In our school, parents or nannies take children to the playground often.
Ideally your daughter could go to the same private school that she's in now. I'm also assuming that's not possible. My daughter attended the same grade school all 5 years and middle school connected to that grade school 3 years. Being able to do this helped build confidence and a sense of belonging. I adopted her and so the first 6 years of her life were chaotic to say the least. And she needed this firm foundation.
If your daughter doesn't have the handicap of tumultuous early years and isn't extremely shy, she will probably adjust quickly with help from you.
Contacting the new school early will be a big help for you. Perhaps you could arrange for your daughter and a friend to visit in the current 2nd grade class. That way she will meet some of the students and know a little about the school. And then you could arrange play dates with those kids during this school year. The usual way that my daughter arranges playdates for my granddaughter is to send her phone # home with the child with whom my granddaughter wants to play. Now that she's in the second grade she writes her own note. Then the parents talk.
Perhaps you can get permission from the shcool to send home a brief note introducing your family and asking their child to get to know your child. You could meet on the playground or in a park so that everyone gets to know each other. In foul weather you could meet at a community center gymn or a child focused restaurant such as Peanut Butter and Jelly's.
I'm glad that you're starting early to help your daughter get acclimated to a new school.