Being a California Native, the Motu days are the best beach day you could EVER have. Better than Hawaii, Better than ZUMA, Cornoa del Mar, or Santa Monica. A full day in PARADISE!

Would your Mom enjoy a week of active island touring and beach/water sports? The PG is mostly that kind of week with some ship time. It's more of a floating hotel than the cruise on the Mariner would be.

But, shipwise, the Mariner is my favorite. 18 days of it, with 6 sea days would be close to ideal to me, and may be even a little too long. Plus, would you really get to visit in NZ and Australia?(I did not look at the full itinerary).