When she "suspects" something is up she can play it off till she "knows" something is up. She can put a key logger on your pc, tracker on your phone, a tile in your car, hire a PI, start taking notes, re-read the Cosmo articles on cheating men and soon she will have your balls roasting on an open fire.
Get some common sense guys. Stop thinking she knows and is just ok with it. Stop thinking she's stupid. Stop thinking you're so smart. Hone your 007 skills, up your game, think like the enemy, be like a Ninja, stealth, leave no trace Grasshopper... Live to fight another day...