If your in the "friends" zone, you cannot expect to get out of the friends zone by being her friend. If you want more and it drives you crazy that you cant have more, you need to STOP being friends.
The best thing to do in this situation is to get her out of your life entirely. For several months if not longer. Someday down the line, when she calls you or you meet somewhere, she will no longer see you as a "friend." Problem solved. Flirt with her, take her out on a date, whatever. If she responds positively, take it from there. If not, cut your losses entirely if you still have feelings for her.
But please, do not do this with the intention of dating her in the future. You need to forget her because there are no gauruntees and you don't want to spend your time worrying over this girl.