You kinda keep ignoring the point that Katie was there because Nami's presence was announced and and leaked to Katie. Nika tagging along was a lucky coincidence (if Katie is interrested in him, which the renders and the was she observed him imo proved).I think it's still important to note no one knew Nika would be there, other than Nami, Mila, Vic, Bella and maybe Nia (can't remember if he told her what he was doing after). Noji didn't know until they left. So who told Katie Nika would be there?
Nami and Nika are obviously related to the Zane's in the same way (however that be, maybe they knew their parents or more probable are their parents but it doesnt matter for the reasoning) so one of them attending is enough for Katie to be interrested to join.
So no, she didnt knew but due to Nami had still an interrest in attending which Noji pointed out as not being a coincidence.