If you do talk, try to concentrate your conversation to the present and future. If she starts bringing up the past, just tell her there is no use in rehashing what you both already know.
Some of her regret could be your happily moving on and having had another girl friend. They want what they cant have. And I also suspect it could be that the luster of the R with the OM has faded.
My XW also had some sort of major girl part operation and I have wondered if it was do to her promiscuous behavior. I do know that she picked up genital herpes from a one night stand.
I wonder if the operation could also be causing some hormone changes in your XW that could be contributing to her confusing behavior to you.
I also got the letter of regret, but that was before the D was final.
You best path is to just move forward and not try to analyze too much of what she is doing.
