For a basic trainer, I'd look at a magnetic resistance unit. The CycleOps Mag gets great reviews, I have the fluid one which is considerably more expensive, but love it.

One option is just trolling her local CL and buy the best rated mag trainer that comes up. That way she can just get a sense of indoor training (not for everyone!) and the relative loudness of the mag (effective, relatively expensive, but loud) before she commits to something new/expensive.