She's done.
What many of us have been preaching for so many months has officially been confirmed. Yamao is Wano's guardian! I thought she'd have the White Tiger, and then after last chapter a Kirin. Primary reason being that these were both powerful mythological eastern guardians and it would fit with Yamao's character as the protector and guardian of Momonosuke. But Oda went above and beyond my expectations and made it explicitly clear for even the slowest ones to catch one. Giving them absolutely no wriggle room.
All those looking for Yamao's role in the crew suggesting maybe she could be the chronicler... or the cabin boy...or the "Oden" of the crew... Here is the role you were looking, being shouted out loud for all to hear.
Her position is the guardian. Not of the straw hat crew of course. But of Momo and Wano. That is where she belongs and that is who she will stay with come the end of the arc.
Oda even put in some symbolism.
The collision of their attacks form a yin yang. A symbol that represents duality and change.
Fire vs Ice
Light vs Dark
Good vs Evil
Kaido is referred to as a guardian deity just like Yamao. This yin yang of change could symbolise the shift from Wano's evil guardian deity to Yamao a good guardian deity.
Either way her chances of joining the crew and well and truly crushed. It would be wild to think Oda would ever give a nakama a devil fruit power that is so explicitly tied down to a single country. Her fruit will always be wano's guardian wolf. The guardian of Wano needs to be with the people of Wano. 2 + 2 = 4.