I'm assuming your sister is talking about the Insignia residential style range that some fifth wheels are now making a standard feature. We have one in our Pinnacle and have not found a down side to it. It cooks and bakes much better than any rv type oven we have ever owned. The temps in the rv ovens were very difficult to regulate which resulted in burned biscuit bottoms. We haven't used the Insignia oven a bunch but it seems to be fairly accurate with the temp settings. I would ask for more details as to what she doesn't like about it.
We tend to use the convection feature on our microwave as much as possible as it does not generate as much heat as the oven does, especially in hot weather when we are trying to help the a/c's keep us cool.