Confronting the Truth

Finding the truth in what is said by a child is not a hard task with my years of teaching experience. I am a good "lie" detector. I am not fond of the word "lie", so I will use "not telling the truth" in it's place. Fortunately, I have found that my 4 year old child does not not tell the truth very often. Yesterday, I was doing some laundry while the baby was taking a nap. She was at the kitchen table plalying with play dough. I heard her feet coming up the stairs and just knew that she was moving on to another activity. She quitely moved into her room, knowing that I was going to ask what she was up to. We are working on cleaning up before moving on to another activity. I asked her if she was done playing with the play dough. Her response was quick, " I picked up my mess already." By her response and sneaking around, I knew that she was not telling the truth. To my surprise, when I asked her if she cleaned up the play dough she told me no and headed back downstairs to do so. What was I to do about her not telling me the truth the first time? I decided to thank her for cleaning up the play dough. I then explained to her that she did not tell me the truth and that was wrong. I told her that is was easier and quicker for her to clean up before moving on and to answer my questions truthfully. She seemed ok with it and moved on. I dread the day that she says things about herself, friends, school. ect. that are not true! What do I do then?