If that's what she wants and she has a reason for wanting it, then that's what she should get. The question is this- Why does she want the Mossberg?
With that said, Benelli is a FAR superior gun to Mossberg. Better build quality, better reliability and durability, and better features and functions.
One thing that I would bring up is that women have a tendency to short-stroke pump shotguns, as do guys with a shorter length of pull. This is particularly an issue with people who are shorter, as women tend to be. If you look at the slide of Nova, you'll notice that the rear of it is extended back a long ways to the edge of the receiver. This is a big advantage to people with a shorter length of pull, as they can hold the slide closer in, and be able to cycle the slide easier. This reduces or eliminates short-stroking tendencies. The Nova was designed to fit a wider range of shooters.
Stoeger is a decent company. They're basically like stripped-down Benellis. The parts/build quality isn't on par with Benelli, but that's because it's the economy version of them. It's like a Honda vs Acura situation.