There are really only two places worth visiting or staying in Idaho:
Treasure Valley and Moscow.
Boise/Nampa/Caldwell/Payette actually has stuff: museums, mall, airport, hockey team, state capital and Moscow is a college/party town, but not the stupid kind.
Honestly, I think Boise is the best of Idaho. I got a chance to wander around downtown and it is still beautiful as ever. If your cousin is into geology, she should spend a weekend in Burns, Oregon. Wrights Point is fascinating and the drive through the Alvord Desert is amazing.
Blackhawk144: Good to see you changed your name and not your attitude!