did you get test kits for your tanks when you set them up, if the wifes tank was not cycled (which it sounds like it wasn't) you will need to be doing water changes everyday, maybe as much as 50% or more to keep the fish alive. If you haven't already, check out those cycling stickys, amonia and nitrite are toxic to fish and they won't last long if either are in the tank. The LFS will usually test water for free until you can get your own kits, if they do, ask for exact numbers, do not just let them tell you the water is ok. They may not know what ok either!!!
Also, once your wifes tank is cycled, I would suggest two more corys (((the same kind that she has one of ))) They are schooling fish, and will be much happier with a couple of friends. Other than that, the tank is fully stocked