What's a girl to do?

Lie!!! Yup my sweet (sarcastic) daughter has entered the lie zone! It was all due to the ice cream sundae party that church had. Since I was teaching for the 1st service and stayed for the second to go in the sanctuary, Abs and Josh got to go to class twice. I made it a point that they will not be getting the ice cream twice. But not little miss, she had two! And what really matters most is that she not only disobeyed my instructions but she lied about it later. Ohhhhh! I am at a loss as to how to handle such duplicitous behavior. I am sure some reading this will think I am overreacting but trust me when I say that this can and will have lasting implications for her in the future if she is unable to correct this wrong. Because make no mistake this is wrong!!!! Any comments of insight would be greatly appreciated.