I messed up entering my response so hopefully it wont double here, LOL.
But since you mentioned God I will go with the assumption you are a Christian. My next assumption will be that you've heard of Veggie Tales, many non-Christians have heard of them too. There is one called Larry Boy and the Fib From Outer Space http://www.christianbook.com/Christian/Books/product?item... It deals with what happens when we fib & how quickly it grows & gets out of control, great movie.
I agree that swift is best. You also want the punishment to fit the crime so to speak. And she also needs to understand the difference between lying & just pretending. I say that because we have always had Santa & the Tooth Fairy. When my 10yo found out the truth about THOSE, he said I had lied to him all those times, ouch! I tried to get him to see we were pretending for fun...but he asked me what the difference was, still hurt the same & that he still felt lied to. So...that was hard to get him to see INTENT, at such a young age, but starting on her now with intent of her lying may help too.
I think removing her from things she enjoys or taking away things she enjoys works well to. Going to their room often is just a ticket to play with their stuff. I wish someone would send ME to my room ever now and again, LOL. But seriously, check out that movie.
Oh one more thing, have you heard of the If Then Chart? http://www.doorposts.net/if_then.asp It is a great tool and it helps you more than your children. You simply list the offense, scripture reference, and then the punishment you & your husband have agreed on. It's put on the chart, hung on the wall, no discussion, no trying to make sure the punishment fit the crime, it's just there for you to follow as well. It's not that expensive & it works great. They also have a Blessing Chart http://www.doorposts.net/blessing.asp that would help reinforce her good behavior which often motivates a child more than the other.
Good luck dear & let us know how it's going.