A compulsive liar will tell lies no matter what. It does not matter what the situation is, he or she will lie. The liar is ultimately out of control. No one is exempt from lying every so often, but a compulsive liar lies routinely about everything, big or small. Compulsive lying is generally a symptom of some greater personality disorder, such as a narcissistic personality disorder or a borderline personality disorder. Telling the truth is hard and uncomfortable for compulsive liars and provides an escape from discomforting situations just like alcohol, sex and drugs do for many people.
Take some time to think about what you will say to a person who compulsively lies. You want to be gentle, yet firm and come to her in a way that might help her receive what you are saying. If you scream and shout at her, it won't help the situation. It will only stir up more strife.
Talk to the person with the compulsive lying problem about different situations that occurred when you knew she was lying. You will need to present your proof so that she will have to face the truth. When you interact with the person who has compulsive lying issues, you will need to present the truth to her every time she lies to you about something. Doing this will help her to deal with her problem often, as well as help her to realize that, yes, she has a problem and that she really needs to make a decision about lying to people.
Be patient with the person. More than likely, she did not become like this overnight. It will, therefore, take some time to get free from this problem if she is serious about it. So, if you truly feel that you want to help this person to get free from compulsive lying, you will definitely need patience as well as the heart and the grace to stick it out.
Tell the person if she doesn't get some real help through counseling or therapy, you will not continue to be around her any longer because she is not only hurting herself, but others as well. Sometimes people decide to finally get serious about getting help when they know they will lose a valuable relationship.
Leave the situation alone. If it becomes too much for you and the person is not seeking help, it just may be time to get away from it all. You cannot force people to get help. If she has the ability to make a decision to get some help and refuses to do so, no matter how hard you try to convince her, you will be spinning your wheels and helping her to hurt you even more in the process.