One thing I would do is help her check her thinking a bit. What would a "real friend" be like? Is she being a perfectionist? Sometimes kids, especially girls, get a very romanticized idea that everyone has a perfect best friend and nothing sort of that counts. As an adults many of us have different friends for different parts of our lives - maybe book club friends, soccer team friends, neighbors, etc. Yes, maybe these are not "best friends" but they are still friends and they still count. So, maybe thinking a little bit about what she can get from friendships she has and can develop even if they aren't perfect. They are still a place to practice being a good friend.