Sorry, Darcy, but that only works if she also increases time (duration) on the bike, assuming the intensity goes down because a road bike is more efficient. I can bike fewer miles on my mountain bike and burn far more calories per hour because it is a more intense exercise. Miles do not guarantee longer duration.

Bottom line, it depends on frequency, duration and intensity. If she gets a bike, any ol' bike, that is more fun than she has now Pooks will probably increase one or more of the above. It's all good.