Hi, C.! I have an 8-year-old daughter, too, and my best advise is to listen. Don't ask her any leading questions (ex: "Are you afraid of being in a new school?" "Do you think the kids will be nice to you?") But just ask if she has any concerns about school that she would like to talk about. Then talk through each one of her concerns with her. Enlist the help of her teachers and other school personnel to watch for interactions between your daughter and other classmates. One thing I've learned is that teachers have always "been there, done that", and often have terrific suggestions to help your daughter along. Teachers will sometimes pair up a new child with someone who knows their way around, so the more familiar child can show yours the ropes. Along with listening, encourage her to try new things at home, and praise her efforts. Believe me, it carries over when she goes to school because you are building her self-esteem at home and her confidence is still there when she is away from you at school.
I'm a single-mother of an only child, and even though my girl has been at her school since kindergarten, she sometimes feels unsure of herself with other kids. But I've notice that helping her feel good about herself when she makes good decisions has helped her come out of her shell at school =)