I'm not even going to pretend that my experience with preeclampsia was anywhere near as traumatic as your experience must have been. In other words, I won't tell you that "I know how you feel"...I don't, so all I'm offering is a dad's perspective.
Based on what I read in your post (and I could have interpreted it incorrectly), your wife is telling you she is ready to try again, but you are definitely not in the same place.
Talk with your wife and find out where she is in the recovery process. I know that she says she is ready again, but try to understand her underlying rationale for trying again. What she says may provide some great input into your own healing process. Then, be honest with her and let her know your concerns. At the end of the day, BOTH of you need to be excited by the possibilities of trying again, not just grudgingly "ready".
As far as determining when you're "ready"...that is really a very personal decision. We each deal with grief differently and I can, again, only speak from my point of view.
When I'm healing from a traumatic experience I don't have a "magic formula" to get my mind back on track. I just "know" when I'm ready to move forward. It's not some great epiphany but rather a combination of hundreds of mental/emotional discoveries and decisions. The "trick" is to know that you WANT to be ready to move on and then each time you are faced with decision, you are making a conscious choice to move towards healing. Don't put yourself on a strict timetable, but always remember what you are trying to accomplish. Some day you want a family and to do that you will have to take on the risk of your wife being pregnant.
In my case (and I know all scenarios are different), I'm a man of faith and I find great comfort in my beliefs. I do spend time in prayer and will talk to other members of the faith community. If you are so inclined, talk with your priest, preacher, etc. and let them know where you are in your healing process and your lingering concerns. You may find that your faith can carry you more than you ever thought possible.
Another thing that can help with peace of mind is to have a world-class perinatologist whom you trust, that you can partner up with during your wife's next pregnancy. The team of the three of you working together can help ensure that your wife and unborn child are having the best care possible, and you can play an active role in her care.
Finally, while you can't force emotional healing to conform to a date/time, there are some very real timeline concerns. Biologically (more her than you) pregnancy only becomes more difficult over time. Also, when you successfully have a child you are making a lifetime commitment. You want to make sure that you are young enough (really it is more about energy) to live up to that commitment. I guess the long and short of it...you can't wait forever.
Good luck with this journey and be strong. Our thoughts and prayers will be with you. Please feel free to send me an email.