I certainly understand your not wanting the affair enabling couple as your child's Godparents.
Just wondering, is your XW still involved with the same OM?
I would think, even though you are DV'd that she would see that it is important that you both agree on Godparents. Maybe each of you could pick one of them. Possibly each of you could chose a close relative from your respective sides. I think that is how it used to be done. For instance, mine were an aunt on my mother's side and a an adult nephew on my father's side. One of my sisters had my mom's 1st cousin and my father's 1st cousin. Traditionally, I think, the Godparents are the folks that are supposed to hold you to your commitment to raise your child to be a good Christian.
Godparents are very important people. They are there to help teach their God child about religion. They should also help strengthen their beliefs. Choosing a Godparent can be one of the hardest decisions new parents need to make.
I wonder if her friends can fill the job.
If she is mainly thinking of who would be guardians should you both die before your child becomes and adult, then it is still important to agree out of respect for each other. After all you are both the child's parents.
It does sound like her mind is made up about this, so I don't know what hope you have of changing her decision. It does sound selfish, disrespectful, and a bit immature of her. I guess it was nice of her to let you know. Did she think you didn't care?
I don't know what faith you or your wife are..whether you are Catholic, Lutheran, one of the Orthodox denominations....here is a link that discusses the choice of Godparents of infants (from a Catholic perspective.
Choosing Godparents of Infants