Many years ago I did some triathlons and endurance rides and learned a few things about riding. CT's advice to use the prowler is, of course, excellent. Another thing for her to do is one the bike strength training. Have her climb hills using a bigger gear. Also, if she has clipless pedals, make sure she has good technique. Clipless pedals allow cyclists to use both legs - the "top" leg can push down on the pedal, as always, but the "bottom" or recovery leg can be used to pull back on the pedal with the hamstrings. A good drill for this is to have her go on a flat surface with no traffic and pedal with only one leg clipped in.