Yumomi (Leona) is a childhood friend of Dawn and Kenny. She sometimes calls Dawn "Dee Dee." She lives near a hot spring with her parents and takes care of three Swinub.
In "Hot Springing a Leak!" she the water from her hot spring was stolen. She later found out that it had been Team Rocket siphoning the water from her hot spring's main pipe. They were planning to use her hot spring water to start their own. Later, she and Dawn defeated Team Rocket and returned the water to her own hot spring.
When she parted ways from Dawn, Ash, and Brock, she told them that she would go and battle in Sinnoh's Gyms. It is unknown if she yet has any badges.
She appeared in a flashback in "Yes, in Dee Dee It's Dawn!" along with Kenny where the reason for Dawn's nickname was revealed.
(Source: Bulbapedia, edited)
