Those Twin Otters are work horses! The fly them onto the glaciers surrounding Denali all the time, albeit with most of the seats removed for the piles of climbing gear.
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I'm more worried about friend wanting to do stuff I'm not comfortable with, such as swim throughs/depths. I suspect she'll be getting buddied up with someone else for at least some of the dives.
In my book, there is no such thing as overthinking.