Lacy was an elderly woman who lived alone in a sprawling mansion. She's best known from the episode "Seeking Shelter from the Storm!" where she appears only in flashbacks and a prominent portrait—having passed away before the main events of the story.
During her lifetime, Lacy formed an unlikely bond with a wild Espurr that regularly visited the mansion. She'd feed it and play with it, and the two grew genuinely close. When Espurr once saw her struggling with health issues, Lacy reassured it and gave her favorite pendant necklace as a keepsake—a precious heirloom she'd received from her husband. It was clearly meant as something meaningful between them.
After that visit, Lacy never returned. Espurr stayed in the mansion for years, waiting and wondering what had happened to her.
When Ash and friends showed up seeking shelter from a storm, Espurr finally had a chance to get answers. The Pokémon befriended the group and asked for their help finding Lacy. That's when Lacy's granddaughter Elise arrived and broke the news: Lacy had died. It hit Espurr hard.
The situation actually led to something positive, though. Elise had originally planned to tear the mansion down, but meeting Espurr changed her mind. She decided to renovate it instead and invited Espurr to visit Lacy's grave with her. Espurr agreed, finally able to say goodbye properly.
Content compiled by AnimeList.moe from publicly available sources.