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Gardenia augusta varieties and Jasminum sambac 'Flore Pleno' are a couple easy to grow Tropicals with a nice fragrance.
Most plants that do well in Hawai'i can't handle cold weather; the plants you bring back most likely will need to be indoors for winter.
On hardyness I can give you any help...best she do is to drive to a location similar to hers in climate (Volcano?) and see what they are growing. She should have a plant guide as to zones with her... No one here in the warm and wonderful growing belt will be able to advise her on hardyness as we don't have to experience it...
Osmanthus fragrans, Kwai-Fah; Citrus limon, Lemon; Crinum augustum, Queen Emma Lily; Phaius tankervilliae, Nun's Hood Orchid; Plumeria rubra, Frangipani; come to mind for fragrance!