I don't think she's joining either but this point is very dumb, man. You should probably delete this one. Ofc there's mention of Zunisha in the journal because Oden went there with Roger and the crew on their journey and we know that their journey is accounted for in the journal. So, Yamato knowing Zunisha makes total sense and it doesn't need to be this big lore secret from the void century or smthn.