Sounds a bit like the legend of King Skjöldr, who was a Danish King who came to the shore as a small child in a boat with no other on it on a shild (hence the name.)
Like Moses, too. Bit of a theme going here. Only, she was an adult already; it's curious that she was presumed royalty like the other two. Perhaps she started her journey as a baby, like Skjöldr and Moses, but people just kept putting a little food in and sending her on her way.
Occam's Razor. It was most likely a lost human from a distant land, speaking another language, traveling in an exotic looking vessel. This is a simpler explanation than invoking extraterrestrial life.
Very much agree that the UFO thing is a red herring. But perhaps Occam's Razor actually points to an even simpler explanation, that of it being a reoccurring mythological trope that was repackaged as an historical event.
That said, I would love if it actually were the case that a mysterious woman from, say, the Dutch East Indies — to make up a random, semi-plausible example — really did wash ashore in a Japanese fishing village. Sounds like a sequel to "The Thousand Autumns of Jacob de Zoet" (awesome book by the way).
Always interests me how legends and stories like this are passed around, and how much changed since the original, but also what /really/ happened for the story to take form.
I wonder if a corrach might explain the description. I've never seen one that was circular, but many have a broader beam than many boats, and an Irish woman would account for the red hair.
