A&A, I guess I change my vote to not go but send a gift b/c if you are really going to be hurting inside and forcing yourself to act happy about the new mom-to-be, then I see no reason to go through that torture. I was thinking, originally, that you didn't want to attend b/c you were so upset with her for not listening to you, and for making the awful decision to consent to circumcision. Because then, I don't see not going accomplishing anything or changing her mind. For your own well-being, you should skip it.
Me? I went to a good friend's baby shower and enjoyed celebrating the whole time. I don't think it crossed my mind while she was opening gifts or visiting with guests to be sad about what was going to happen to her son's penis in a couple weeks. I'm just being honest here, and as much as I agree that circ'ing is horrible, awful, unnecessary, and dangerous (etc.) it's not something I dwell on whenever thinking about an acquaintance's new baby.
Anyway, here's hoping for a miracle and that your co-worker changes her mind before her son is born.