I would look for a new job as well.
Since ignoring her won't work I would turn the tables on her and find ways to torment her, but do it in ways that she can't prove or do anything about. You know be just as juvenile as her. I also agree with finding people at your workplace that can't stand her and maybe you can dig up some dirt on her, or find ways to provoke her and make her go nuts and get fired. Sure she can make up stuff and tell the bosses, but in reality she probably already has.
Life is too short to be miserable at some mundane job, because some chick is pestering you and trying to push your buttons, at least have fun with it. It's quite obvious that your workplace isn't going to do anything about it. This chick is untouchable like you mentioned, a tape recording of her saying something isn't going to get her fired. You going into your supervisors office to complain about her makes you look bad like you can't get along with people, even if it is all her. It will escalate until someone gets transferred, fired, or she finds someone else to pester and leaves you alone.
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