Trixabelle "Bella" was a female human who attempted to destroy Tranquility Spa as revenge against her mother Kane for ignoring Bella's childhood and leaving her to care for her father.
When Dregs attacked the spa, Bella and Kane stayed behind to fight them, giving the Thirteenth Doctor, Graham O'Brien, Ryan Sinclair, Yasmin Khan, Nevi and Sylas time to escape. (TV: Orphan 55)