Why are girls so mean?

I hope that everything I write doesn't sound like I am always complaining, but I have something to gripe about today.  Ashley has a friend who likes to "joke" the problem is that Ashley doesn't perceive it as a joke and comes home from school really upset.  So before school this morning,  I took it upon myself to talk to this little girl and tell her its not kidding or joking unless everyone in the situation feels like they're in on the joke, and asked her if she would try to be a bit more subdued when it comes to Ashley in her "joking".  My conversation with this little girl lasted for a total of a minute and a half .  Right after school I got a call from this girls mom telling me that next time I wish to speak to her daughter she wants to be there.  I apologized and told her exactly what I said and in the manner that I said it.  She told me that it was part of her daughters nature to be a joker and that if Ashley didn't like it she didn't have to hang out with her.  The problem is that this girl will not leave Ashley alone... but she is just "joking".  I have told Ashley that maybe she needs to find a different friend to hang out with, but Ashley is so sad.  I hate this growing up thing.  Why can't kids be kind to each other.  I just wished every body loved my children as I do and saw them the way I see them.  It hurts when they hurt.  I wish I knew what to do.  I guess I will just have to let things settle themselves.  I hope they d0.