Nami is 100% a Descendant of Zaza (Or a previous DF holder like Joyboy was to Nika)
Title says it all. I've always been a proponent of the theory that the reason Nami shares the exact same face as Vivi, Shirahoshi, and Rebecca is that it's foreshadowing that she's also a princess. And considering her main character trait is that she's supernaturally good at predicting the weather and literally creates rain as her main ability, I think her connection to Zaza might as well be confirmed. She definitely has a connection to Zaza but she obviously doesn't have the DF so her being a descendant makes the most sense.
Personally my theory is that Nami is either a descendant of Zaza from back when the gods were real, or a descendant of the DF user of the Zaza fruit during the Void Century that was probably kept in the royal family. I think the destruction of Nami's homeland might have something to do with Dragon getting the Zaza fruit if it does end up being true that he has it (which I'm not 100% convinced about)