Liza is the caretaker of the Charicific Valley, which is made specifically as a natural paradise for wild Charizard.
Liza made her debut appearance in Charizard's Burning Ambitions (EP136). Ash's Charizard wanted to train at the valley seeing the other powerful Charizard there but Liza refused after it lost to her Charizard, Charla. But seeing its determination to train there, she agreed.
Liza made a brief cameo appearance in the third movie with Charla and other Charizard from the Charicific Valley.
Liza later appeared in Great Bowls of Fire! bringing Ash's Charizard with her. It was revealed that she was good friends with Clair since they were young children. Liza often takes the Charizard from the Charicific Valley to Blackthorn City in order to train them.
Ash would also call Liza sometimes whenever he needed Charizard sent over.
(Source: Bulbapedia)
