After been through this myself, I see NO advantage of pretending to be stupid in this sitch.
What is the advantage in letting her know that you know? You'll feel better about yourself. If you don't say something, you'll be angry at her AND yourself. You know she's lying and she thinks she's getting away with it. Not that she won't find a way to lie after she knows you know -- they always do. Least that's what I think.
I know it's difficult because technically you're separated -- but if it is no big deal, why isn't she being truthful with you? She's hiding it cause it is a dig deal.
