In the same narrative as this question, a private ketch sailing the South Pacific will make landfall in Australia about midday on Tuesday (13 Sept 2016). As they were preparing their documents, the captain grew worried that one of the passengers is a Russian national, i.e., a person who would normally need a visa to land in Australia. It's not a case of a stowaway, she is an invited guest.
She has a US Tourist Visa which is still valid and joined the cruise in Hawaii several weeks ago. Nobody thought to consider the bigger picture. Their previous port of call was Honiara where, apparently, the party was able to land without producing travel documents. I suspect Australia will be more rigorous. It's too late to turn around and yeah, everybody should pay more attention to these things, but sometimes it happens. I have no clue about corner cases arising under the Australian system.
So what happens now? Can she get a visa-on-arrival? Or she be unable to land? Or worse, taken into detention? Or is it OK given they already landed in Honiara and she has a current US tourist visa?