While I agree with the point on quality, constant aperture zoom lenses tend to be MUCH more expensive than variable aperture lenses. Your single lens costs more than twice her entire starting kit :) They also tend to have fairly specialist zoom ranges. I find it hard to imagine somebody with a constant aperture zoom lens would find benefit in this camera simulation. The majority of the kind of people using it will be beginners with kit variable aperture lenses.
The most common advice for them would be to get a prime lens. Especially in this simulation that offers both distance and focal length setting (which are, for this scene and 18-55mm focal length, mostly interchangeable), I'd like to have it. It'd also allow you to go (cheaply) to f/1.8 or f/1.4, which would be much better to illustrate the effect that aperture has on the depth of field. With a common f/3.5:5.6 kit lens and APS-C sensor, you won't get a shallow DOF and nice out-of-focus background easily, and that could be frustrating to a beginner. Especially when you learn to do it in this simulation.
The faster aperture tends to necessitate better glass, but the idea that only fast lenses have good glass would not necessarily be true. There are plenty of "slow" lenses that have very good optical quality.
