I used to feel the same way when my kids first went to school. I found that in prep the kids tend to play in big groups and don't play one on one until they become more comfortable. So even if she's saying she hasn't made friends she's probably played on the playground or sat in the sandpit with everyone in her class.

Perhaps you could organise for her to pick a friend to come over for a play after school, or even go to the park after school with a few other mums and their kids.