It all depends upon how much she rides on it, how much power she puts out, how quiet you need it to be, how long you want it to last and how hard it is on the rear tire.

In my book, there are only a couple of them out there to consider. I ride 3000-4000 miles per year and train during the winter months about half that on a trainer, rollers or spinning classes. I would look at the Cyclops Fluid 2 trainer. It is very quiet and will last her for many years. It is the "Standard" out there, if there is such a thing. It has a good flywheel, so it is smooth. It also has a fairly large diameter road wheel (where it contacts the tire), so it isn't quite as hard on the rear tire. Note that all trainers are hard o nthe rear tires and wear them down. I use a cheap rear tire in the winter for training or a worn out racing tire, so I am not ruining my expensive good tires.

The other nice thing about this trainer is the way it adds resistance as you increase your gear size. It adds resistance in such a way that it get harder faster as you reach the taller gears. Thsi is exactly how a bike acts in real life out on the road. I do have a magnetic trainer also (my old one) but it doesn't act that way and it is anything but quiet, as it whines pretty good.

It may be a bit more expensive than what you were looking for, but you do get what you pay for.