Madison Throne from book club (sg) could be Sven's gf(wiab).
About theory that Summer-Leya's daughter,possible but don't forget that there are not so many young models and it can be just coincidence.
But I also have a little theory about Summer. Considering what a lustful dog Willie is, and the whole family there are definitely not prudes, then it’s like a minefield in SG. Go figure out who is who’s cousin, uncle,sister etc.
So, what if it later turned out that Summer is very close to Nike, as Nami and the others, including Najiko, decided to separate them. This is what Najiko is hiding.