Just read up on your sitch. Your recent post about finding text messages over "years" to the OM talking about marriage? Did I read that correctly as in she has been talking to this guy for years discussing marriage? I was under the impression her A was fairly new.
You do not have to show her what exactly you found out, and how. It is best to let her guess what you know. Knowledge is power and you do not want to handicap your future ability to gain more knowledge. I do agree with the comment Mozza made referencing Starsky. Calmly let her know she is lying, and she knows she is lying. Remind her that you made it very clear the boundaries and she broke them.
Me: 42 W: 32 Married 7 years together 8.5 S1: 7 S2:7 Bomb #1: 09-16-13 Recon #1: 11/13 A discovered 04-03-2014 W filed D 05-19-14 but never served me I filed D 12-02-2014 S 05-31-14 Divorced 5-19-16