Lizzie Applegate was a singer/songwriter from the 19th century who wrote many famous plays such as "The Bandit's Treasure", which was also a song (Nancy sings this song in Shadow Ranch). In Message in a Haunted Mansion it is revealed that, after marrying Diego Valdez who turned out to be El Diablo, she hid the Great Christmas Gold in their house in San Francisco that Rose Green came to own in 2000. She set up a series of puzzles in the house for him to solve in order to find the gold, but he never came back to the house, leaving Nancy to solve the puzzles. Lizzie probably died around 1905, since the house was bought in 1906. Her will stated that if Diego was not found a year after her death, her estate would be liquidated.
Elizabetha and Diego married on June 18, 1876.
Lizzie was a huge contributor to the Ladies Protection and Relief Society, and arranged for the money used to buy the house after she died to be donated to the organization in its entirety.
Nancy can also read about Lizzie at the Paseo del mar High School library in Secrets Can Kill: Remastered.
In The White Wolf of Icicle Creek, it is revealed that Lizzie frequented Icicle Creek Lodge and was friends with Trapper Dan. A picture of her is also on the wall of the Canute College Homestead in Trail of the Twister for some reason.