I think many of you are missing something...
She says that she needs to move the lever a lot farther in order to get much braking power. Granted, you get less braking power with the rear brake, but I don't think that's the issue. To me, this says that the cable is too loose so that she's having to pull the lever far towards the drops for her liking before the pads are gripping the rim. Looseness of the brakes is personal preference, though I can see that having tighter brakes with short fingers could be useful (I like my brakes loose, but I do not have small hands).

Turn the barrel adjuster at the rear caliper counterclockwise to tighten the cable and bring the pads closer to the rim. It will now make contact with the rim with less modulation of the lever.