The best thing for your daughter to do is go onto individual airline websites and / or flight search engine websites (Kayak, Webjet etc) and use the "multi city" search function to see what airline options and prices are available.
The Maui leg will add a fair bit onto a more standard Melbourne - NYC or Melbourne - LA return flight plus internal flights, so while it can probably be done cheaper doing it yourself, I don't think $2800 is *that* insane of a price.
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