And interesting piece, Amy. Since I was a kid, I have always had friends who were girls, as your friend did with you. This has continued all of my life.
Over the years, I have sometimes had the line crossed in both directions (friends who became lovers, lovers who became friends). I still have one female friend who has been a platonic friend since elementary school.
I currently have far more friends (no hanky-panky involved) who are women than men.