She first appeared in the episode May, We Harley Drew'd Ya!. It was revealed in the episode that she had defeated Drew in his very first Pokemon Contest, which caused him to cry. Since then they seem to have become friends. They see each other often in Contests and they also keep in touch. She also noticed that Drew became more competitive, and she thinks May is the reason for this.
She also saw Brock often when he was still the leader of Pewter Gym, and he knew her from before as well.
Solidad stated that she is old friends with Harley, and that she finds him to be an interesting person.
She competed against May in the Kanto Grand Festival, which she won. In an interesting comparison, May also cried after being defeated by Solidad. She was last known to be traveling in Johto and in Staging a Heroes' Welcome!, she made a cameo appearance along with Harley and Drew, watching May perform at the Wallace Cup.
[credit to bulbapedia]