Can she connect it to her PC? If so, you can probably use the browser plugin from Garmin to send the coordinates on geocaching.com to the Garmin. Though, I'm not sure that the 'eTrex H' can support that. Good Luck
For those of you with devices that cannot read .kmz's natively.....
http://garmin.gps-data-team.com/poi_manager.php
lets you supply a kmz file (or one of several other types) and it will convert it to gpx (or other formats) online, for free.
FWIW, GPScity.com has a bunch of stuff like replacement battery covers, and replacements for the clip, and the adaptors to hook to handlebars. I also picked up a RAM mount for handlebar mounting and I'm pleased with that too.
I am new to Garmin, but echo your sentiment.... is there a third-party app (for purchase or otherwise) that knocks the socks off Mapsource and Basecamp? I LOVE Google Earth but it only has the most basic integration with Garmin devices. And I know about EasyGPS, and a couple other rudimentary "waypoint loaders". I'm wondering if some enterprising developer has gone the extra mile the Garmin developers didnt in coming up with a full featured waypoint/track/route/POI maintainer that tightly integrates with most of the (huge array of) Garmin devices.