When I said for you to make it clear how you feel, I didn't mean go seek her out and TELL her. In fact, you already HAVE told her. I meant more like IN CONTEXT -- like Mark says, when it comes up -- do not minimize or "it's okay" her infidelity or her decision-making.
But certainly don't go picking a fight.
I meant to DEMONSTRATE that you're not okay with what she's doing, but DEMONSTRATE that YOU will be okay.