Can a convection microwave be used to dry fruit
I would guess that you will get a the same limited success for a couple of reasons.  

You might not have the correct heat required.  Food dehydrators usually have an operating temperature around 140 degrees Fahrenheit.  If you can get your convection oven to go that low, I don't think you would have a problem with accidentally cooking the food.  

Heat however is only the first step.  Dehydrators only use heat to coax the moisture out of the foodstuff.  The key ingredients you are going to be missing is the air-flow and ventilation.  A crucial component to de-hydrating is quickly removing the moisture (released by the heat) from the air surrounding it.  The air flow allows for a higher evaporation rate since the moisture inside the food will be in a disequilibrium with with air surrounding it. The ventilation supplies the surrounding space with a constant supply or dryer air effectively maintaining disequilibrium. The greater the disequilibrium, the faster the food be de-hydrated.

If I were you, I'd make her happy and go get a good dehydrator with adjustable fan-speeds.