Shirley possesses an extremely inquisitive mind, causing even the normally reclusive Norikata who normally strictly obeys the practice of keeping magecraft secret to trust in a complete stranger to a large degree. Although mostly a boon, the old saying, "Curiosity killed the cat", causes her to bring about a tragedy. She displays a cheerful temperament, gentle attitude, and virtue. In finding Kiritsugu's name to be too complicated to pronounce on a regular basis, she nicknames him "Kerry." Due to that he constantly helps her with shopping and other errands on a daily basis, the villagers she him as her younger brother, much to his disappointment with his budding feelings of love for her. Feeling close like family, she views them as her own father and younger brother.
She greatly admires Norikata, although she understands that he is not a normal person and the reasons for the villagers' guarded nature towards him and his reclusive ways. She believes that he has come to the island simply for the sake of being away from the city for his research, amazed by his knowledge and discoveries that she feels could change the world if even one of them were released. Knowing that they still need to remain secret, she is hopeful that they'll be able to be put to use. Kiritsugu notices that she becomes much more mature and sensible for her age when speaking of his father.
Shirley was born as a native of Alimango Island, growing up in an extremely poor educational environment that did not even allow for her to attend elementary school. She relied on the teachings of Father Simon, the local priest, to learn reading and writing, but that was enough to stimulate her ample intellectual curiosity. She was able to obtain a Master's Degree through correspondence courses by the age of thirteen, causing Norikata Emiya to take an interest in her as an assistant when he arrived with his son, Kiritsugu Emiya. She became put in charge of handling the Emiya household's miscellaneous daily tasks like cleaning and shopping, picking up traces of magecraft due to Norikata not bothering to hide his true nature from her. Four years older than Kiritsugu, she became close friends with him. Still close with Father Simon, he often lectured her that working in their household would cause her to be "ensnared by the devil", giving her a silver knife and telling her it is a useful talisman with which she should never part.
Before the eventual tragedy of Alimango, Shirley explains the origin of the island's name to Kiritsugu while driving an old, rickety pickup truck necessary for reaching the faraway Emiya household. Discussing the perception the the villagers have of Norikata, she mentions that Father Simon speaks badly of him, showing Kiritsugu her knife. She is hopeful his discoveries can be put to use in the world, noting that Kiritsugu could make them successful even if Norikata has already given up on the idea. Kiritsugu, jealous of her as her father's "favorite pupil", scoffs at the idea, but she claims that Norikata has yet to show her anything important and that Kiritsugu will be the one to truly succeed him. She asks about his aspirations for the future, telling him that he will have the power to change the world. Telling him that she will always be beside him until she can confirm the answer with her own eyes, he can only bashfully look away from her.
In hoping to prove the validity of Norikata's immortality experiments, she drinks one of his experimental regents. Though he had told her that it was dangerous and that the Dead Apostle being unable to control their urges would make it a failure, her curiosity won out over her. Kiritsugu searches for her throughout the next day until he finds her in a henhouse at the edge of the village, having massacred the chickens for blood. Filled with anguish and about to "die", she begs for Kiritsugu to kill her with her silver knife. Too scared to kill herself, she weeps for him to do it while there is still time. He is unable to act, and as she bites her own wrist in frustration, he runs away from her, believing something would save her. The entire village is eventually infected and cleansed by the Mage's Association's and Church's Enforcers and Executors after Kiritsugu tells Father Simon of her condition.
As his first love and reason for pursing his notion of a "hero of justice", she has an impact on Kiritsugu for the rest of his life. He is greatly torn over the fact that killing her would have saved the islanders, giving him the motivation to kill his father, and later Natalia Kaminski, to prevent further tragedies. Greatly impacted, he promises her that he will never let such an event occur again. Taiga Fujimura reminds him greatly of Shirley, causing him to pamper her greatly during his final years of life. As he dies, he remembers her asking what he wanted to be when he grew up, remembering her smile and gentleness, and unknowingly speaking his promise of wishing to become a hero of justice before peacefully expiring.
Shirley's talents in learning, enabling her to obtain a master's degree at thirteen despite a poor educational environment, cause Norikata to take an interest in her, receiving some training from him. It is not enough to be considered on the level of taking her as a disciple, only the basics of the basics mostly taken from interacting with her without hiding his nature as a magus. Her innate curiosity allows her to absorb his words at a great pace, citing that he possesses exceptional intelligence and talents. He says it is a waste for her to be left on the lone island, expecting great results from her in the future. She manages to copy an experiment involving stopping the flow of time for a flower by mimicking him, causing him to remark on her talent as a magus. It fails, causing her to remark that she will never be more than his assistant compared to Kiritsugu who will succeed him. She owns a small silver knife given to her by Father Simon, citing that it must be "something very precious" due to its sharpness and ease of use. Simon calls it a very useful talisman that should never part from her, but she mostly just uses it for peeling fruit.
She turns into a Dead Apostle after drinking one of Norikata's experimental regents, barely holding onto herself before becoming something inhuman. Her skin becomes white as wax, veins popping up around her make her looks change drastically, and it causes her to seek out blood from chickens. She eventually turns to humans, causing the entirety of the island to be turned into ghouls.