Lizzie moved with her parents to a new neighbourhood. After a lonely first day at her new school, Lizzie returned home and packed some peanut butter sandwiches and ran away to be with her old friends.
As she marched through the woods behind her house, she discovered the Doctor's TARDIS and wandered inside, amazed to find it bigger on the inside. After Lizzie accidentally dropped one of her sandwiches into a slot in the console, she hid as the Thirteenth Doctor entered and attempted to take off, only for the TARDIS console to malfunction. Lizzie rolled out from under the console as the TARDIS shook, and the Doctor spotted her.
After Lizzie revealed to her what had happened, the Doctor (eventually, after using the random generator button) brought the TARDIS to the planet Plorp, home to the friendly Glorp species, who the Doctor explained were fantastic engineers who could help them fix the TARDIS.
As the Glorp got to work, Lizzie befriended the smallest of them, an orange Glorp called Blorp, and the two bonded over their shared love of their peanut butter sandwiches. This gave Lizzie the idea to have Blorp squeeze into the slot in the control panel to eat the sandwich she dropped, successfully solving the problem. The Doctor eventually returned Lizzie home, who had secretly smuggled Blorp off of Glorp in her rucksack. Lizzie reunited with her parents and returned to her bedroom, where she and Blorp had the "best sleepover ever". (PROSE: The Runaway TARDIS)
Lizzie was a young, dark-skinned child. She kept her hair up in a bun with a pink hair band, and wore a blue hair clip. She wore a bright teal jumper with big yellow stars on it. She also wore magenta coloured tights with black shoes, and a pink rucksack. (PROSE: The Runaway TARDIS)