You have not screwed anyting up, don't beat yourself up.
I would play it cool and casual and see what happens. If nothing else, you could use it as an opportunity for her to talk and for you to listen. I would validate and be respectful and polite. Who knows what she may tell you?
I would not play "hard to get" as that feels artificial, but clearly your DBing efforts are working and she is very interested in you.
For me - the elements of reconection include:
Has the affair ended? Does she want to work on the marriage with you? Does she ask for forgiveness for her recent behaviors? Will she go to marital counseling with you?
Fingers crossed the conversation goes well.
Again, I am no expert, but these are just my thoughts.
