Well I think you need to ask yourself what you hope to accomplish by pressing the point. If she denies meeting up with him and you prove that you know she is, now what? Where does that leave you.
If she says "you're right I'm wrong you caught me in a lie" how do you feel after that and how does she feel?
Sometimes our motivation for wanting the WAS to admit they are attached to someone else is to make it real for us, and other times because we feel a perverse need to punish ourselves.
There's really nothing to be gained from either other than an extremely temporary sense of satisfaction followed immediately by feeling worse.
If you have a different motivation that's fine -- just think about it in advance.
Usually in this case your perceived win is actually a personal loss.
Acc
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015