Cecile grew up with her parents Miles and Leyte in Bellheim Apartments with next-door neighbors Guy Bannings and his younger brother Lloyd. They immediately became very close, and spent so much time together that Cecile considered both of them part of her family. Though it took a while due to Guy's denseness for him to understand Cecile's feelings for him, he eventually became Cecile's fiancé. She also has been friends with Ilya Platiere since Sunday School.
After Guy's death and during his funeral, Cecile suppressed her sadness, put on a calm air and smiled to support Lloyd. Since she considered Lloyd as part of her family, and because Lloyd had lost the last member of his family, she felt that she had a duty to watch over him. Later on, Lloyd would cite Cecile's support as one of the key reasons that he entered the police force.
Although a natural airhead, Cecile is an incredibly open-minded person. Thanks to her kind and caring personality, the doctors and head nurse at St. Ursula Medical College often rely on her to relay messages to patients. When Crossbell falls into chaos or panic, she never loses her cool and always looks out for all of her patients.
When monsters attacked the Medical College during the Cult Incident in S.1204, Cecile showed her strong sense of responsibility by intending to sacrifice herself so that her patient, the young boy Mikhail, could escape.
Cecile's strong devotion led to rumors among colleagues that she might be the reincarnation of St. Ursula whom the Medical College was named after. The same St. Ursula was the source of inspiration for the novel The Saint and the White Wolf.
Whereas the fictive St. Ursula meets a tragic end, the saint she was based on married a knight and lived on. Zeit, who serves as the inspiration for the White Wolf in the story, told the Special Support Section that St. Ursula's descendant was still alive today and working at the hospital, implying that Cecile is actually the descendant in question.