I guess it depends on what temperature you're looking to keep your freezer at. But the way a temp controller works is you plug the controller into the wall outlet and the fridge into the controller. A temperature probe from the controller than goes into the fridge and the controller cuts the power on and off depending on the temperature you set.
So, just thinking this through, if you plugged the fridge into the controller, set it at 32 (for lagering, not lager fermentation) and put the probe in the freezer portion, it would turn the unit on until the freezer got to 32 and then shut the whole thing down. What you set the fridge internal temp at wouldn't really matter, it would shut off and on with the freezer. You could put a room or fridge thermometer in it just to track the temp and see if its staying cool enough for your wife's purposes.
If you set the freezer for lager fermentation, usually around 50F, then its almost certain the fridge portion would not get cold enough for storing food, or at least as cold as a fridge usually gets.