I can totally relate. I was just like your wife. DH and I have 2 bio boys. DS #2 was born with a congenital heart defect (that was surgically repaired) and I was diagnosed with a seizure disorder shortly thereafter.
We were advised not to have any more children. We were told that I might not live through another pregnancy, and if I did, there would most likely be major birth defects in my unborn child.
We really wanted another child, but the risks were too great. I needed time to "grieve" the loss of my fertility. DH compiled all the information on adoption so that it would be available when I was ready.
I, too, had concerns about bonding with a child I didn't carry. I am here to tell you, I bonded with Jasmine with no problems whatsoever. I journaled during the whole process so that I could feel connected to her. As soon as we received our referral, she was mine. I knew that I could pick her out of the 3 billion people in China if I needed to.
As soon as I held her, it was as if we had always been together (on my part anyway, she wasn't so sure of me for a few days...).
Good luck -- you can invite your wife to check out this forum, as well if she would like to talk to any of us!