How Do You Stop Being Friends With Someone?

I need to know how do I stop being friends with someone? The person is constantly cancelling or changing plans without any notice or without even asking. One major example is we have been talking about seeing Hollywood Undead at Summerfest (this Friday) since J Dog and Funny Man said that they were coming here on their Ustream back in January (I think) but suddenly she cancels. The worst is though, I asked her what the plan was for Friday on snapchat so she clearly ignored me because she read it and never replied. Five hours later I text her asking what's the plan my dad's wondering and she says we aren't going anymore. That's not the only time she's done this. There have been numerous sleepovers cancelled, several bonfires where she said it'd be me and her then she invites several other people, movie plans changed on multiple occasions, and there are many more. So my question is if anyone has advice on how to end a friendship; How do I end this friendship? She (was) my best friend.