sony in ear noise canceling headphones. ~150 dollars. ear buds block noise and are ultra efficient, player output quality more important then power. u have enough power to go deaf using ear buds on any player. don't get big headphones for working out, sop up sweat and all the nastiness...and bulk is bad.
if you must amp
http://www.headsave.com/ here are some quality units

or if u want to drive audiophile cans
and get her a solid state mp3 player, 256-512mb versions are out that are decent. discmen don't go well with working out, bulk ick! iriver 256-512mb are good, includes fm too.