How can I make my child understand that lying makes me distrust everything she says? She really thinks it's OK to lie and when she is confronted, she just lies more. I've tried everything from extreme punishment to ignoring the problem. I'm afraid one day she will end up in prison. Please advise me. She is 17 and thinks she can't get caught. Thanks for the advice.
Let me put this as clearly as I can. You failed to teach your daughter basic moral principles and your chance of instilling them at this late date is about nil. In nearly every location, except my own state of Nebraska, a teenager is considered an adult at the age of 18 (in Nebraska it is 19).
You have testified as to why this has happened. First, you admit that you were inconsistent in your treatment of lying. Thus you raise a gambler who sees sins as things worth the risk because she is able to get away with them. Second, you didn't teach her that lying was wrong. You are only concerned that it makes you feel distrustful of your daughter. At 17 your daughter doesn't care about your feelings all that much -- she is far too wrapped up in her own imaginary world.
With such a foundation, there isn't much to work with. You can start by being consistent, but you only have a few months before she will be out of the house. You can't erase 17 years of wishy-washy child rearing in a few months. Since you use your own changing feelings as a standard for morality instead of God's rock-solid word, there is no reason she, or anyone else for that matter, will care what you say. It is fairly clear that your daughter has no true belief in God. She has no fear of eternal punishment. She probably doubts there is such a thing as sin.
And here you want to wave a magic wand and make it all better.
The best and probably only thing you can do is let her face the consequences of her lies instead of shielding her as you have been. From here on out, do not accept a single thing that she affirms. You don't have to explain why, just don't trust her. If she asks, tell her that liars aren't trustworthy people and leave it at that. If she gets in trouble, let her handle her own problems. If she brings her problems home, such as drugs or any other illegal activity, then move her that day out the house and tell her she is on her own. Until you show some backbone, she has no reason to even consider changing her ways.