Quote Originally Posted by bcipam

Uncertain why the shop told you to ride in high gears. If that means you are rotating the pedal very slowly, then that's wrong. I can ride in a high gear and still rotate the pedal at 80 - 90 and am moving very fast - usually 19 - 22 mph. If you find yourself going say 8 - 12 mph and in high gear, gear's too high, lower it! Of course as you hit a grade you also lower the gearing in order to maintain the cadence.

FYI - if you can find one - try a computer with cadence to help you learn.
Maybe she was originally riding in too LOW a gear. That could be miserable too.
and 80-90 might be a desired cadence, but it's not that easy for beginners!