Yes, currently it is not clear if Ayua is a Zane, but the avaiable evidence hints that way. Her features are proof that at least Miru is her Mom and Kati Zane is provenly (by dialog) her aunt. There is a possibility that Miru´s younger sister is her Mom, but why would she stay in Wollust? She has less incentive to stay there than Miru had. Even Willi was not truly convinced in the beginning that he (and Miru) would stay in Wollust long term.I understand your logic, bro. But the fact that Ayua is the daughter of Miru and Willy is not yet a fact, you forget that Miru has a younger sister.
We are fans of Katya, we love younger sisters very much, you know what I'm talking
About, so as you can see there are a lot of options
Only the Ocean knows the truth
I think Ocean is covering the bases for several possible WIAB endings to be "true", depending on how the player played WIAB. We have a girl among the SG clique who looks very much like a younger Daphne, Ayua we already mentioned, I am sure we will see Leia´s kid(s) sooner or later, Dana´s too.
Considering how controlling Leia is and how deep their (Willi/Leia)feelings where, there will be hints in SG for both when Willi did not return her feelings anymore and when he did so. Ayua´s existence in Wollust is a hint that Leia and most likely Miru found a way to live together, since Willi and Miru were prepared to leave if the pressure would be too strong. And a pissed off Leia can be scary.