I'll also caution you to remember NOT to be drawn into a fight about this. There are many reasons. Her knowing that you snooped will be counter productive, for one. She will just get better at lying, for another. You will lose the limited information you have today. And, last, it's a fight. Fighting is counter to your goals. You don't want to fight. Fighting just increases her resolve and makes her think she's doing the right thing.
Last, but not least, she already knows she's lying. She doesn't need you to point that out.
