Yoyo is Mashiro's grandmother, and a well known scholar back in Sky Land.

A major incident has occurred in the peaceful Sky Land!? The young Princess Eru has been kidnapped by the monsters of Underg Empire! A brave young girl, Sora, follows the princess through a mysterious hole. "TV"? "Cars"? Are those some kind of magic tools!?!?
 
But there's no time to be surprised! She has to get the princess back to the castle...! Flying between two worlds! The adventure with the Pretty Cure begins now!
 
It's hero time!

A movie celebrating the 20th anniversary of the Precure franchise, featuring characters from all 20 series so far!

The theme of this year's Pretty Cure is “The Expanding World." This is an exciting and fun slice-of-life story about Sora Harewataaru, who came from Skyland to Solarseed City, and Mashiro Nijigaoka, a resident of Solarseed City.
 
(Source: Kodansha, translated)

Yoyo Nijigaoka