Others have made good points. Like them, I think your WW is not sincere either.
I don't think the sex they made that weekend developed spontaneously. On the contrary, as I have said before, she might specifically brought up the subject during the counseling, so she would prevent your objection. Whole was planned.
Being drunk doesn't excuse her. But put that aside, why do two people whose primary purpose is a racing event drink so much? Can we really think they're there for the race?
We all know that drinks are indispensable for romantic nights. They are part of it, they don't turn an ordinary night into a romantic one.
The claim that there is nothing but friendship before sex is absurd, the claim that after sex, considering it as never happened and remaining friends is much more absurd.
It's normal for her now to think that many of the things she does are stupid. Yeah, not smart enough to save her ass and after all, she got caught.
So why didn't it seem so stupid to her when she was doing all this? She knew that you were suspicious, suffering, what she had done was wrong and will end your marriage. So the conditions for her to see all the things you say she is aware of now were exactly the same then. Then why now? Because she thought it would work and now see it didn't. In fact, she realized nothing new, she was well aware of everything.
What should we think now? Did she finally get it? Or is she trying new stories that she thinks will work this time? Why should we think that this is another phase? She lied, you didn't buy, so she tries new lies, she can't go back and stick to the old story and say that they didn't have sex.
I have no doubt that she wants to stay married to you right now. I've never seen any WW ask for a D after getting caught unless she has an exit A.
But is this the real and permanent version of her? I don't think so.
When the storm subsides and you return to routine, she will complain about the same or new different issues. Don't think that that time she will show a more understanding and different attitude, because she learned from the past. You will encounter the same reckless, cruel, selfish person, this time closer to the exit from marriage.
She's ready to do anything to fix you now, right? So ask her to stay away from you as the person who did all this evil and is the source of your great pain. What keeps this pain alive is her presence. Will she accept a divorce without any resistance?
Seemingly even the most remorseful WSs don't want to accept a solution in which they are not involved. This leads us to the fact that there is almost no such thing as real remorse, and what looks like this is actually another form of WS selfishness.