You want to put a lot of exposure pressure on this woman too... Make sure everyone at work knows this woman is attacking your marriage and you have invited her to back off but she refused.
Her "I don't know what to say" is a passive aggressive "no"... Assume she has refused and act as if she rejected your offer.
The OW needs the fight taken to her doorstep.. Expose to her parents if you have to.
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712