She starts the same way she did with the elder girls:
"Have you noticed that your daddy and I seem to be able to do some things that other people can't?"
"The oracles at Sinai have to know this, because instead of being a god, Jovah is a spaceship." (Isabella has always told bedtime stories about spaceships, pretty much specifically to prepare for this revelation.) "Sometimes something goes wrong with it, and then it needs to be able to tell an oracle to come fix it. So Alleluia told me her secret, and I told her mine, and I went up to the spaceship, and it wasn't very smart at all. It could talk, but it didn't really understand things; it only did what the settlers told it to do, and what it heard prayers for. I didn't think it was doing a very good job of being a god, but all I had to do to make it listen to me was just a little bit of magic, and now I'm the spaceship's captain."
Ariel nods again. It is quite obvious to her that her mother's natural place in the scheme of things is captain of their god.
"We found the restaurant a few more times, and we met more and more of me, and of Daddy, and of some other people none of whom you've met," says Isabella. "And then we met one of me who had a computer-person that was much smarter than Jovah. Her name was Jane, and she moved into the computers on the spaceship, and she had the power to pick up anyone she could see and put them down in any place she could see, even between universes. So all of us could visit each other whenever we wanted, and not have to wait for Milliways to appear, and we could have parties, and coordinate on large projects, and share magic. But then, well before you were born, when Damaris was still a baby, Jane broke - Jane's soul lives in the one of me from her world, and that person was attacked, and it hurt Jane. While Jane was broken, time started passing differently in different worlds. Her own world had three seconds go by while ten years passed here."
"But then Jane got better, and we all celebrated, and we found some more people and added them to the group - several of me are a peal of Bells, several of Daddy are a deck of Jokers. And during this time your older sisters both got to meet everyone, and there are others of them, although their parents only have two children so there was not one of you, then. There might be now, I don't know."
"Would the other of me have my name, or a different name?" she wonders.
"A different name, at least if she were from that family. Because Rose - that's that Bell's nickname - already knows what you are called, and wouldn't want to make it difficult to keep track of you. She named her Damaris 'Dominique', but she prefers her middle name 'Yseult', and she named her Keziah 'Céleste'. I don't know what she would name a third child but it wouldn't be Ariel and might not be a Samarian name at all."
"It can be very confusing. Luckily no two of the Jokers use the same name and Bells don't have a hard time choosing nicknames, but it became difficult with a few other repeating people."
"All kinds of things, but the next part of the story I'm telling you is that Jane broke again. A little over a year ago. We don't know when she'll be back."
"That's why your uncle Nathaniel left. He was visiting another Joker, in a world called Aurum, when it happened, so now he can't come home until she's better. He's safe, though."
"Most Jokers don't have others of Nathaniel, though there are a few," says Isabella. "And... your uncle is the only one of the few who is nice."
"They are bad people. They hurt some alts of Daddy and of me very badly. I was very worried about Nathaniel, when I found out who his alts were, but - he seems to be fine."
"Yes. They are not themselves very nice, and Nathaniels don't react to that the same way that Jokers do."
"And it's secret from people who don't know it," says Ariel. "And you and Daddy and Alleya and Keziah and Damaris know it. And Nathaniel but he's not here."