There's only one explanation for why Tashigi did not appear during Wano: The arc was more about the Kozuki family and reclaiming the country. Everything else was secondary.
For Tashigi to be involve in the arc in a relevant capacity, Wano would have to focus on other aspects. More on the ramifications of its isolation, the immigrants who settled outside of the country, and more on the country's history and culture and how all of those relate to Tashigi, and I guess Zoro, to an extent.
But that's not the arc we got, which is a shame, since I would've preferred a less war oriented, more lore centered arc for Wano.