I'm not trying to make you feel worse, but just stating what I have observed in people. It seems whenever we tell something bad that happen many years ago.....folks don't get as upset as they do if it was in the present. I'm talking about relative.....not your W. You & your W did not get the guidance you needed. I think that has a lot to do with her bringing up the OW. She probably tried to leave it alone, but wasn't able to let go of it. Fourteen years is a long time to keep unforgiveness in a heart and pretend nothing is wrong. I can see her bringing it up for several reasons, but until she can work through it, I don't know that you are going to be able to help her. She really needs a professional to work with her.......both of you, really. Do you see her A having anything to do with what happen 14 years ago?
I believe it must be harder for women to let go of some things than it is men.....IDK. Men seem to look at the facts of the matter and women look at emotions. You may be thinking, "It was just sex" and she may be thinking, "But how did you really feel about OW" and it doesn't matter that you may have told her that you didn't love OW......deep down she still wonders about everything and how you "really" felt. JMHO.
If she refuses to go to C, then I really don't know what to tell you about her bringing up your A. Would she listen to you now....since it wasn't discussed back then?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!