Regarding why she should would walk off at that time and maybe get off the ship:
> I don't think there was any intention to meet Yellow. Having already left him at 3:30, the chances of arranging to meet him again a mere 2 or 3 hours later is remote. Who does that?
> If she stepped off the boat voluntarily, we can surely rule out going to a bar to continue partying. It would have been 6-7am and she already declined an offer of going to a bar once docked with another staff member "because they're creepy"
> Which would leave only stepping off for a brief period, so brief that she didnt consider it worth leaving a note. Perhaps to fetch beer or cigarettes. She didnt plan to be gone long.
If all those criteria are met, I can only really see a scenario where she was followed - or accosted - during her brief excursion, whether by staff member, a predator on the dock or maybe even a dodgy taxi driver. It happens.