This issue really is Spirit Airline's problem. Their website is not set up to accommodate reservations that are not originally made on it. I have had travel booked through them by my corporate travel agent and experienced the same problems you are having. Their telephone service will have you waiting on hold for hours. I hung up after 1 hour 30 minutes. (On speakerphone while I was doing other tasks.) I requested my travel agent correct the issue for me and she had the exact same problem.

My suggestion is to get to the airport early and hope for seats next to your wife.