I agree that you should probably leave. Because even if she does stop lying, it will probably take a good amount of time for you to trust her. You will still always be wondering if shes lying or not. Your partner is the one person you should not lie to and should be able to trust. In my past experience, if you don't have that, it just won't work.
Sounds like she can't get herself to stop lying, so I doubt you are going to be able to. If it is as bad as you say, and you just can't take it anymore then it is probably time to cut your losses and move on.
Lieing isnt good. You will not believe her what she is doing she sounds like a impulsive liar. She probably doesnt relize she is lieing.......I would sit down and talk to her tell her you notice she been lieing to you and you will not be able to believe what she says........If she doesnt STOP lieing I wouldnt be with her anymore cause you will get fed up.How long you been with her? How old?