My opinion: she knows. And she remembers. You don't have an affair and suddenly forget all the details.
Now, you can "choose" to bury them, but they are there, and can always be unburied.
The question you need to ask is WHY she claims she doesn't know. My guess is that she did something she thinks you will find very distasteful or even a deal-breaker if you found out.
Part of that, I guess, is to decide what is a deal-breaker for you. Is there something she can claim to have done during the A that will make you end R and move on?
That's the tough one. In some ways, you have allow the WS to feel like the R will be possible with complete honesty, and only complete honesty. And then, you have to decide if, no matter what you hear, you'd rather hear it all (no matter how offensive). If you are ready to go ahead with that mindset, then you really need to let her know that, and stick to it.
You're allowed to react to it, show pain, anguish, anger, etc. You can tell her you feel hurt and betrayed, and even sickened. But it all gets thrown on the A pile and, in a way, opens to road for reconciliation.
For me, the sex and touching wasn't as hurtful as some of the things she admitted she told the AP about me, or told him about how she felt about him. When it is out, the WS is allowed to be ashamed of it, and that's important. They need to be ashamed of what they did and said. But if they are allowed to hide it, never tell it, they never feel shame for it...and that is a bad thing moving forward.
Me: BH, 48
Her: WW, 43
Kids: 20,16,16
D-Day (E/PA): 6/02 (rugswept)
D-Day (PA): 7/11/07
R-Day: 9/16/07
D-Day (EA): 6/17/12
D-Day (E/PA #2): 1/29/16
Filed for D: 2/2/16
Divorced: 6/14/16