Lies

What do you do the day that you find out your child has outright lied to you? We caught her in a lie today. We are not naive enough to believe it is the first one...but sad enough that it was proven. This has always been a very large issue with me. I hate lies(as I'm sure most people do). I guess that I'm supposed to learn forgiveness and trust. How do you trust someone that you don't know very well and that you know hasn't been completely open and honest with you? And why am I the one learning all the lessons? I'm the adult!!! Shouldn't it be the other way around? I'm sure all of my mother's generation would laugh up a storm at this.....but dang it.