Friend? or a fake? friendship or not?

[The_Chick_that_will_silence_YoU]

Have this friend,who never comes out with me and my other friends. She always stands up. Always says "im coming" "few mins away" but 2h later,shes not there. When were at school, she acts as if nothing has happend. My other friends in my friendship group, cant stand her when she does this.
Obviously, we wont be angry if she cant come but its the constant let downs and broken promises.
I always get answers like "she doesnt want to hang out with you" well, If me and my main friends werent hanging around with her, she'd wouldnt have anyone. Really, my best friends are Jess,Sami,Isha and Katie. I used to consider her as a best friend but the lies got to me and now i dont even know if i can call her a friend? Possibly, in the 3 years we've been 'friends' shes come out 4times... and the other(God knows 100times) she says shes coming but never comes.
If its the day before we're going out, she wont answer my texts,calls,bbms,facebook,twitter..anything. She tries to hide that she's read them but really she has. For instance : BBM shows if someones read the message or not.. and its always says read next to my messages sent. Another example is TWIITER, she'll say that "she hasnt been on all week,and didnt get the message" but really, shes constantly updating her twitter? What do I say to her? Im 14 btw.

[Brett]

"Always says "im coming" "few mins away" but 2h later,shes not there. "

Have you ever called her out, and actually asked her straight out, like "WTF? What happened? You said you was on the way, so what happened to you"?
Ask her what the real problem is, and if she doesn't want to hang out with you or if the problem is with one of the others in the group?
Is there something else going on in her personal life? (problems at home?)
Then just stop asking her to join you. She obviously doesn't want to hang out or be your friend.
Give it up.