Ahh, I think I got it now. Thanks!
I was confused, because I was thinking that the 8606 form was supposed to include both of our contributions combined. That's why I was thinking that part of the conversion (2012 contribution made in March 2013) wouldn't be recognized until 2013 taxes, so the pro rate rule might include the wife's tIRA contribution when calculating the taxable amount converted in 2012.
I guess it would have helped if I would have read the first line on the 8606 form that says "If married, file a separate form for each spouse required to file Form 8606."
Thanks again for the help!