So, she got into boating. That makes sense then. I had previously thought that her randomly deciding that she now wants to be an explorer and leaving her family behind after her character motivation for the past several seasons had been centrally focused around getting home to her family with no interest in travelling the larger world was a massive plot hole and just plain shitty writing, but now I see that I was wrong and it was all properly set up.
Sorry, but like Dany's needless cruelty, that also did not come out of nowhere. It came out of "no one". Back in Season 6, when she was training to be "No one", she had the following exchange with the actress from the play who she refused to poison.
Lady Crane asks Arya to travel with them to Pentos.
Arya declines, and when Lady Crane asks her where she'll go, she replies, "What's west of Westeros?"
Lady Crane says she doesn't know, to which Arya responds, "Nobody does. That's where all the maps stop."
Lady Crane says "The edge of the world", and Arya says, "I'd like to see that".
Also, I don't think simply getting home to her family accurately reflects her motivation throughout the series. Back in season 4, Brienne came to bring her to her family and she ran away from her and away from her remaining family to go to Braavos instead to learn how to be an assassin so she could kill those on her list, which was her real motivation for most of the series. Once everyone on her list was dead, she returned to the idea of exploring what was beyond the known as she'd mentioned two seasons earlier. More generally, playing a normal expected family or societal role was never part of her character. Her desire to go off and do her own thing and see what's beyond what is known seemed rather in line with her nature to me.
Perhaps b/c a rewatched all prior seasons just before this one, I saw more of the "set up" of this and of Dany's destruction that others are saying were random and out of nowhere.