Is your main issue that she had a PA or that she is lying? Because if a PA isn't a deal breaker, then maybe there is a way to discuss this and say that while you understand that she might be trying to spare your feelings, that a PA wouldn't be a dealbreaker and right now, let's get everything on the table. If she says she has told you everything, then you need to decide if you can trust that. Not immediately, but that is the deal. But remember, trust is built. After something like this, it may be impossible to freely give it, but maybe built again.
Just my two sense. I hope some peicing vets can help you.
M: 9 yrs T: 13 yrs H:34 Me:35, S4, D2, S 7 months Dday 11/12-PA & multiple PAs Dbing 12/12 S 1/13 7/13 H moved back in basement. 8/13 #3 born 10/13 still cheating 10/13 He moves across country, I file for D