Infidelity, for the BS especially, is a trauma. Several of the books and articles I've read have stated that the trauma of infidelity is right up there with war and death in terms of how much of a "job" it does on our psyches. In fact, some state that it is actually worse than either of these things, because war and death are inevitable, however, infidelity is a choice, and a betrayal. In that regard, infidelity might actually be one of the worst traumas a human can experience, because it is so very purposeful and personal. I think that's really important to understand. Our BS's aren't "hurt". They are devastated. Decimated.
But it gets worse. Do you know the difference between PTSD and Complex PTSD? In a nutshell, most people, even though they have trauma in their life, have some sort of support system to fall back on. A spouse, a loved one, family, a good friend, maybe a preacher or teacher. So they have trauma, but they also have non-trauma in their lives. But what happens if you don't have a support system, or any sense of safety whatsoever. What if your life is non-stop trauma with no break in between? THAT's complex trauma. It's the difference between sticking your hand in a blender, and sticking your hand in a blender and leaving it there permanently.
So think about this for a moment. If your spouse has the acute trauma of infidelity foisted upon her, and at the same time, has her biggest support system (you) ripped away from her, and actually becoming the source of her pain instead... then she's left with no support system, no break, no way to get out from under that trauma in the ways that she always been able to up until now. Nothing really makes sense to her. She has to rebuild everything, from scratch, with no handbook, and no support. That sounds like complex PTSD to me.
We've all seen the made-for-TV versions of PTSD, usually it is portrayed as a soldier who freaks out at every loud noise and who turns to alcohol and drugs just to try and deal with it all, or who has these "flashbacks" and thinks that things are going on now, even though they aren't. Is any of this starting to sound familiar with what's going on now in your relationship?
Trauma gets "Stuck" in our brains until it has a chance to process. If it doesn't process, it stays stuck and causing problems. Removing the PTSD is work for a therapist, however I can tell you this much. Part of the work means acknowledging and processing the trauma. But how can you process the trauma, when it is still occurring? You can't. Which is why things such as TT do SO MUCH DAMAGE to our BS's. They not only reinforce the old trauma, but they add new trauma on top of it. And what's worse, it is lie after lie after lie, and after a while, the BS can't trust anymore. And if you can't trust, you can't process, because you need some sort of baseline of safety and sanity to hold onto.
In my opinion, the reason she can't be here in the now is because she hasn't adequately processed the past, so when a trigger comes up, the flashbacks are for real. She doesn't trust you yet. She might want to, but she can't. I know there are some things that you have "agreed to disagree" about sort-of, and that's fine, but that might leave some issues stuck.
I know this might not be the answer you want, but in my mind, the best way to move past this is to just keep on doing what you are doing. Work on being honest. Work on being present. Work on being authentic and not buried in shame. It's less about what you specifically do and more about consistency and accountability. Your wife will process the trauma when she feels safe enough to do so, and the more often you DON'T get defensive, the more often you do what you said you would do, the more often she feels empathy from you, or sees progress in you, the closer she might be able to getting to the point where she can trust you and talk to you about that stuck trauma. And when she processes it, she'll lose the need to keep going back.
I can tell you from my own experience that once that switch flipped and my head popped out of my ass, our relationship changed almost overnight. You could almost watch her walls (and mine) come down. The moment we could discuss things like two rational and present adults, the moment she could tell me how she felt and I could hear her without making it all about me instead, it all just changed. And if I'm to be honest, the moment my walls dropped, I felt like such an idiot, because it was just so damn simple, and yet it was something I had not been able to do until that moment. I started to talk and walk and act like the man she married, and she responded in kind.
If you haven't, I'd suggest getting a copy of "The body keeps the score" and perhaps read it to each other, daily. Just a few pages a day, and discuss what you read. That's all. It's a simple exercise, but in doing so, you'll not only learn more about PTSD and its affects, but you open up opportunities to discuss things, thoughts and feelings and ideas, in a non-confrontational setting. Once you can talk to each other about anything, you can accomplish anything.