I don't know.. I believe if you "pursue" her, she could end up fence sitting. Which in your case may be an improvement.
Here is the problem I have with Plan A.. she is in the throws of an Affair/Relationship whatever you call it. Think about when you were in that position.. it consumed you.
Worse yet, you may end up becoming a friend that she confides in .. do you want to hear the sordid details? Probably not.
I believe your case is a "See.. I can do it too" situation. Let it cool off. Let her have some space. Trust me.. she's looking to see how you react.
There is a third place that some guys have hit on called "making her happy.com"
It basically calls you a puss the whole time and tells you to be a man.. Caveman type stuff. I think it really depends on your sitch. Although, I see lots of commonality here.
