She first appeared in the chapter where she was in the cave when Pietra took Ash and his friends there. Later, after Pietra caught a Rhydon for her tunnel project, she took her grandmother to a nearby town and celebrated with Ash and his friends after the project was complete.
In the anime
Pietra's grandmother was only mentioned in Right On, Rhydon! when Pietra mentioned that she needed to complete a tunnel for her grandma to have access to a nearby town.