Brunwine was among the early flesh eaters who had crashed on Earth at some point before or around the 1500s. Being the oldest among them, she served as their leader, her only concern being how to keep her people alive and fed. She first encountered the Thirteenth Doctor in Guelder, where she took a bite out of her arm. After consuming the Doctor's Time Lord blood, Bethany realised she had begun to age at a much slower pace, resulting in her continuing to live for centuries, watching her friends grow old and die as she did. Throughout her extended life, she raised "generations" of children, and continued to learn more about the humans her people had been preying on, to the point that she had taken a liking to them.
In the 2010s, Brunwine, now residing in London, began her historical podcast series, Hidden Human History, which talked about the lesser-known conflicts of Earth's history, inspired by the Doctor's prior statement about history: "all of the actual people get lost in the numbers and the names". Brunwine explained it all to the Doctor, along with Ryan, Yaz, and Graham when they all paid her a visit at her home in 2019. (COMIC: Hidden Human History)