At this stage, I would leave the girls to sort it out. It's quite possible that this incident will be forgotten by this afternoon and your intervening will only create a bigger issue. It is difficult to watch your child struggle to find their place, but you can't be there to sort out her friendships for her - part of school is social learning which develops resilience and independence. Perhaps you could invite some of the kids over for a play date - one at a time - to allow your DD the opportunity to build friendships.